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200M/06-99-991212 


GENERAL    BIOLOGY 

A    Book  of  Outlines  and  Practical  Studies 
for  the  General  Student 


By  JAMES  G.  NEEDHAM,  Ph.D. 

ASSISTANT    PROFESSOR    OF    LIMNOLOGY    AND    GENERAL    BIOLOGY 

IN     CORNELL     UNIVERSITY 


WITH    64     PRACTICAL    STUDIES 
287  TEXT  FIGURES,  AND 
9   PORTRAITS 


ITHACA,   N.  Y. 
THE  COMSTOCK  PUBLISHING  CO. 
1910 


Copyright,  19  io 

BY 
COMSTOCK    PUBI^ISHING   Co. 


TO     THE     MEMORY    OF 

JOHN        GORE 

MY  TEACHER  IN  THE  DISTRICT 
SCHOOL,  WHO  FIRST  TAUGHT  ME 
THE  USE  OF  A  PRINCIPLE  AS  A 
TOOL    OF    THE    MIND. 


.  19705 


PREFACE. 

This  book  offers  a  series  of  practical  studies  of  biological 
phenomena  for  the  guidance  of  the  general  student.  It  is 
not  a  formal  text,  and  not  at  all  a  treatise,  but  only  a  guide 
intended  to  assist  the  student  in  acquiring  for  himself  some 
real  knowledge  of  living  nature.  It  differs  chiefly  from 
other  books  intended  for  the  use  of  college  classes  in  the 
wider  range  of  studies  it  offers,  some  important  phases  of 
biology  having  hitherto  been  dismissed  with  mere  didactic 
instruction.  Morphology  has  dominated — often  monopo- 
lized— college  work  in  biology  in  the  past;  doubtless,  be- 
cause it  was  first  reduced  to  pedagogic  form,  and  made 
available  for  laboratory  instruction.  A  more  equable 
treatment  is  here  attempted,  in  the  hope  of  leading  the 
student  to  a  practical  acquaintance  with  elementary 
phenomena  in  the  whole  broad  field. 

The  generation  of  biologists  which  began  its  studies  with 
Huxley  and  Martin's  pioneer  laboratory  manual  has  wit- 
nessed a  marvelous  expansion  of  biological  knowledge. 
Departments  have  sprung  up,  and  teachers  as  well  as  prac- 
titioners have  specialized,  and  courses  have  multiplied 
amazingly.  Yet  I  am  persuaded  that  the  reasons  given  by 
Huxley  and  Martin  for  offering  a  general  course  are  as  valid 
today  as  they  were  in  1868.  Indeed  I  am  inclined  to  think 
that  some  added  reasons  have  grown  out  of  the  increasing 
applications  of  biological  knowledge  to  the  practical  affairs 
of  life.  The  conditions  of  our  living  make  ever  increasing 
demands  for  knowledge  of  life  phenomena,  and  some  com- 
prehension of  biological  principles  is  fast  becoming  a  part  of 
the  common  intelligence. 

V 


vi  GENERAL  BIOLOGY 

We  are  organisms;   and  out  of  that  fact  grow  the  funda- 
mental relations  that  general  biology  bears  to  a  whole  wide 
range  of  special  sciences,  the  threshold  of  which  may,  I  hope, 
be  reached  by  those  who  follow  the  course  here  outlined. 
After  Chapter  I,  which  is  introductory,  the  studies  of  chap- 
ter II  should  lead  up  to  physiology,  algology,  mycology, 
bacteriology,   protozoology,   etc.,  those  of  chapter  III,  to 
morphology,  comparative  anatomy,  embryology,    palaeon- 
tology and  special  botany  and  zoology ;  those  of  chapter  IV, 
to  cytology  and  eugenics;    those   of  chapter  V,  to  ecology, 
and  limnology;   those  of  chapter  VI,  to  pathology,  experi- 
mental biology,  etc.;    those  of  chapter  VII,  to  neurology, 
psychology,  sociology  and  ethnology.     And  in  the  broader 
sense  of  these  terms  many  more  special  sciences  are  included. 
In  the  preparation  of  this  course  I  have  had  in  mind  the 
needs  of  the  great  majority  of  college  students,  who  may 
hardly  spend  more 'than  a  year  in  this  subject.     Certainly 
no  other  subject  touches  their  lives  at  so  m.any  important 
points.     What  will  best  serve  their  needs  ?  has  been  the  ques- 
tion constantly  before   me;     not.   What  has  been  taught 
hitherto?     Ecological    and    evolutionary    phenomena    are 
just  as  available  for  practical  studies  as  are  morphological 
types,  and  I  have  introduced  them  freely,   although  not 
without  pangs  of  regret  for  the  good  things  of  former  courses 
that  had  to  be  omitted  to  make  room.     I  have  reduced  to 
a   minimum   the    directions    for    the   laboratory   study   of 
morphological  types,  for  excellent  outlines  are  everywhere 
available  for  work  of  this  sort;    and  I  have  given  a  larger 
place  to  outlines  for  field  work  and  experimental  studies.     I 
have  arranged  the  subject-matter  to  suit  the  seasons  of  the 
college  year.      I  have  included  more  than  a  year's  work  in 
order    that    selections    might    be    made.     For    pedagogic 
reasons,  I  have  introduced  at  the  first  phenomena  of  some 
familiarity,    postponing    more    technical    matters.     Mere 


PREFACE  vii 

technique  has  no  part  in  this  course.  Facts  are  neither 
better  nor  worse  for  educational  purposes  because  of 
technical  difficulties  that  may  or  may  not  stand  in  the  way 
of  their  acquisition;  and  therefore,  other  things  being  equal 
I  have  given  preference  to  such  observations  as  are  most 
likely  to  be  continued  after  the  work  of  the  college  course  is 
ended. 

The  purpose  of  the  introduction  given  for  each  subject  is 
to  orient  the  student  for  the  work  assigned — not  to  replace 
the  lecture  or  the  recitation.  I  have  tried  to  tell  what  he 
should  know  in  order  to  outline  what  he  should  do;  and  I 
have  tried  so  to  shape  the  conclusion  of  his  work  as  to  invite 
a  little  thinking.  During  the  past  seven  years  I  have  been 
seeking  methods  that  would  facilitate  the  handling  of  bodies 
of  facts  sufficiently  large  for  satisfactory  illustration  of 
general  biological  principles  and  phenomena.  Many  new 
exercises  have  been  tried  by  my  classes  in  field  and  labora- 
tory; the  ones  that  have  proved  most  serviceable  are 
included  in  the  following  pages.  Herein  are  detailed  the 
methods  I  have  found  most  available.  The  materials  used 
are  of  less  consequence.  I  have  used  whatever  lay  nearest 
at  hand,  only  seeking  to  draw  my  materials  from  a  wide 
range  of  groups,  in  order  to  extend  the  acquaintance  of  the 
student  with  the  face  of  nature.  In  so  far  as  it  has  been 
necessary  to  touch  upon  theoretical  questions,  it  has  been 
my  purpose,  not  to  advance  any  biological  theories  but  to 
bring  the  student  into  practical  contact  with  the  facts  under- 
lying all  the  theories. 

The  field  of  biology  is  so  vast  that  no  one  can  claim  expert 
knowledge  in  any  considerable  portion  of  it.  It  is  very 
probable,  therefore,  that  in  covering  so  much  ground  in  even 
so  elementary  a  manner,  I  have  made  some  mistakes.  I 
can  only  hope  that  they  may  not  be  of  such  nature  as  to 
seriously  mislead  or  confuse  the  student  and  that  I  may 


viii  GENERAL  BIOLOGY 

have  the  further  aid  of  generous  colleagues  toward  their 
early  elimination.  • 

Many  of  my  colleagues  and  former  pupils  have  helped  me 
with  valuable  suggestions  and  I  would  be  glad  if  there  were 
space  to  thank  them  all;  and  I  cannot  refrain  from  making 
mention  of  the  special  help  that  has  been  given  me  by  Pro- 
fessors J.  H.  Comstock,  W.  A.  Riley,  G.  F.  Atkinson,  B.  M. 
Duggar,  B.  F.  Kingsbury,  I.  M.  Bentley,  A.  Hunter,  R.  H. 
McKee  and  Drs.  A.  H.  Wright  and  W.  A.  Hilton  on  the 
part  of  the  proofs  that  they  have  seen.  Others  of  my 
colleagues  have  generously  loaned  me  valuable  portraits, 
concurring  in  my  belief,  that  it  would  be  worth  while  to 
introduce  the  faces  of  at  least  a  few  of  the  great  pioneers 
of  biology  unobtrusively  into  the  students'  intellectual 
environment. 

This  book  exists  for  the  sake  of  the  practical  studies  con- 
tained in  it.  Mere  attendance  on  a  lecture  course  does  not 
amount  to  much;  for  in  biology,  as  in  other  subjects,  it  is 
only  those  who  handle  the  raw  materials  and  build  up  with 
them,  who  can  ever  really  comprehend  the  superstructure. 

James  G.  Needham. 


CONTENTS. 

CHAPTER  I. 

THE  INTERDEPEXDEXCE  OF  ORGANISMS. 

I.  The  Relations  Between  Flowers  and  Insects,  p.  7.  i. 
The  adaptation  of  flowers  to  insect  visitation,  p.  1 1.  2.  The 
adaptation  of  insects  to  flower  visitation,  p.  17.  How  to 
know  the  orders  of  flower  insects,  p.  24.  3.  The  relative  fit- 
ness of  the  different  visitors  to  one  kind  of  flower,  p.  26.  4. 
The  relative  fitness  of  the  different  flowers  visited  by  one 
kind  of  insect  to  profit  by  its  visitation,  p.  28.  5.  Precise 
adaptation  between  flowers  and  insects,  leading  to  mutual 
dependence,  p.  29.  6.  Specialization  miscarried,  p.  32. 
II.  Galls,  p.  35.  Animal  galls,  p.  38.  The  animals  that  produce 
galls,  p.  42,  Key  to  the  commoner  insect  larvae  and  mites 
found  in  galls,  p.  45. 
III.  The  Relations  Between  Ants  and  Aphids,  p.  47.  The 
chance  feeding  by  ants  on  the  honey  dew  offered  by  aphids, 
p.  48;  The  habitual  guarding  of  aphid  colonies  by  ants,  p.  49. 
The  domestication  of  aphids  by  ants,  p.  50. 

PRACTICAL   EXERCISES. 
Study  I .    Floivcrs  adapted  to  insect  visitation,  p.  14. 
Study  2.    Insects  adapted  to  visiting  ftowers,  p.  24. 
Study  J.     The  relative  fitness  of  the  different  visitors  to  one  kind  of 

flower,  p.  26. 
Study  4.    An  examination  of  all  the  flowers  visited  by  some  cotnmon 

insect,  p.  28. 
Study  5.    A  case  of  precise  adaptation ,  p.  J2. 
Study  6.     A  study  of  common  galls,  p.  46. 
Study  7.     Observations  on  ants  and  aphids,  p.  54. 

CHAPTER  II. 
THE    SIMPLER    ORGANISMS. 

I.    Some  Typical  Alg^,  p.  56.     The  cell,  p.  61.     The  form  of  the 
plant  body  in  common  algae,  p.  64: 
II.    Some  typical  protozoans,  p.  68. 

ix 


X  GENERAL  BIOLOGY 

in.  The  Life  Process  in  Plant  and  Animal  Cell,  p.  82.  Mat- 
ter, p.  82.      Energy,  p.  83.      Protoplasm,  p.  88. 

IV.  Some  Intermediate  and  Undifferentiated  Forms,  p.  91.  i. 
Plants  that  lack  chlorophyl,  p.  92.  Molds  and  other  fungi, 
p.  95.  Bacteria,  p.  97.  2.  The  slime  molds,  p.  loi.  ^. 
The  flagellates,  p.  104. 

IV.  Reproduction  Among  the  Simpler  Organisms,  p.  109.  Cell 
division,  p.   109.      Sexual  reproduction,  p.  112. 

PRACTICAL    EXERCISES. 

Study    8.     The  cell  of  Spirogyra  and  the  protoplasm  of  Nitella,  p.  60. 
Study    g.    Observations  on  cell  form  and  growth  habit  in  algcB,  p.  Oj. 
Study  10.     The  structure  and  activities  of  Paramceciiim,  p'.  72. 
Study  II.     The  specialized  cell  bodies  of*Stcntor  and  Vorticella,  p.  76. 
Study  12.    Observations  on  cultures  of  yeast  and  molds,  p.  g6. 
Study  I  J.     A  few  observations  on  bacteria,  p.  100. 
Study  14.     Observations  on  slime  molds,  p.  loj. 

Study  75.     A  comparative  examination  of  common  flagellates,  p.  107. 
Study  16.     Observations  on  reproduction  among  the  simpler  organisms, 
p.  11^. 

CHAPTER   III. 
ORGANIC    EVOLUTION. 

I.  The  Plant  Series,  p.  1 18.  Bryophytes,  p.  118.  Alternation 
of  generations,  p.  124.  Pteridophytes,  p.  128.  Speramato- 
ph^-tes,  p.  142. 

II.  The  Animal  Series,  p.  156.  The  hydra,  p.  157.  The  earth 
worm,  p.  163.  The  salamander,  p.  179.  Development,  p. 
193.  Types  of  nurture,  p.  214.  The  life  process,  p.  217. 
Common  features  of  development  in  plants  and  animals,  p. 
218.      Systemiatic  classification,  p.  221. 

II.  General  Evolutionary  Phenomena  as  Illustrated  in 
Briefer  Series  of  Organisms,  p.  222.  i.  Divergence  and 
convergence  of  development,  p.  222.  Homologies  and  analogies 
p.  223.  The  veins  in  the  wings  of  insects,  p.  225.  The  serial 
homology  of  the  higher  crustaceans,  p.  230.  Phylogeny,  p. 
236.  Convergence,  p.  243.  2.  Progressive  and  regressive 
development,  p.  245.  Palaeontology,  p.  246.  The  persistence 
of  the  unspecialized,  p.  250.  Regressive  development,  p. 
251.  3.  The  correspondence  between  ontogeny  and  phylogeny, 
p.  255.      Why  evolutionary  series?  p.  264. 


CONTENTS  xi 

III.  The  Processes  of  Evolution;  Attempted  Explanations, 
p.  266.  Natural  selection,  p.  266.  Variation,  p.  267. 
Mutation,  p.  273.  The  struggle  for  existence,  p.  276.  Arti- 
ficial selection,  p.  279.  Orthogenesis,  p.  281.  Segregation, 
p,  283.  The  interaction  of  external  and  internal  forces,  p. 
286. 

PRACTICAL   EXERCISES. 

Study  17.    An  examination  of  bryophyte  characters,  p.  12'/. 

Study  18.    Fern  development,  p.  140. 

Study  ig.     The  general  structure  of  the  fern  sporophyte,  p.  141. 

Study  20.    A  comparison  of  developmental  features  of  other  pterido- 
phytes,  p.  141. 

Study  21.    Spermatophyte  structure,  p.  154. 

Study  22.     Spermatophyte  development,  p.   1^4. 

Study  2j.     Observations  on  the  structure  of  the  hydra,  p.  162. 

Study  24.     The  general  structure  of  the  earth  worm,  p.  lyS. 

Study  25.     The  cellular  structure  of  the  earth  worm,  p.  179. 

Study  26.     The  ijtternal  organs  of  an  amphibian,  p.  206. 

Study  2J.     The  structures  of  the  body  wall  in  an  amphibian,  p.  207. 

Study  28.     The  cellular  structure  of  an  amphibian,  pp.  208. 

Study  2g.     The  early  development  of  an  amphibian,  p.  2og. 

Study  JO.    Determination    of   homologies    in    three    series    of   closely 
allied  insects,  p.  22g. 

Study  J  J.    Observations  on  plasticity  of  form  and  persistence  of  type 
in  Malacostraca,  p.  2jj. 

Study  J2.    An  attempt  at  interpreting  a  possible  phylogeny,  p.  2j8. 

Study  jj.     A  comparison  of  convergent  species,  p.  24J. 

Study  J4.     The  ontogeny  of  organs  in  the  frog  or  salamander,  p.  261, 

Study  j^.     Fluctuating  numerical  variations,  p.  272. 

Study  j6.     The  struggle  for  existence  among  seedlings,  p.  278, 

CHAPTER  IV. 
INHERITANCE. 

I.  The  Visible  Mechanism  of  Heredity,  p.  289.  The  history 
of  the  germ  cells,  p.  296.  Fertilization  and  maturation,  p. 
299.  Parthenogenesis,  p.  204. 
II.  The  Observable  Results  of  Inheritance.  Types  of  in- 
heritance, p.  308.  Alternative  inheritance,  p.  310. 
III.  Nature  and  Nurture,  p.  318.  Inheritance  of  acquired 
characters,  p.  318.     The  meaning  of  nurture,  p.  321. 


xii  GENERAL  BIOLOGY 

PRACTICAL   EXERCISES. 
Study  27 •     Observations  on  cell  divisions  and  on  maturation  of  sex  cells, 

P-  305- 
Study  j8.     Observations  on  parthenogenesis,  p.  jo6. 

Study  JQ.     Observations  on  the  relation  between  fecundity  and  nurture, 

P-  325- 

CHAPTER  V. 

THE  LIFE  CYCLE. 
I.    Alternation  of  Generations,  p.  330. 
II.    Special  Methods  of  Asexual  Reproduction,  p.  331. 

III.  Change  of  Form  With  Alternation  of  Hosts,  p.  340. 

IV.  Metamorphosis,  p,  342.      The  transformations  of  insects,  p. 

343.      Internal  metamorphosis,  p.  347. 
V.    Artificial  Division  and  Combination  of  Organisms,  p.  353. 
Regeneration,  p.  353.      Grafting,  p.  360. 

PRACTICAL   EXERCISES. 

Study  40.  Observations  on  asexual  reproductive  methods,  p.  JJ7. 

Study  41.  External  metamorphosis  in  insects,  p.  J46. 

Study  42.  Observations  on  internal  metamorphosis ,  p.  35/. 

Study  4J.  Experiments  with  regeneration  in  planarians,  p.  j6o. 

Study  44.  Grafting  practice  with  plants,  p.  j6j. 

CHAPTER  VL 

THE   ADJUSTMENT   OF   ORGANISMS  TO   ENVIRONMENT. 

I.  Adjustment  in  Place  and  Time,  p.  369.  i.  Local  distribu- 
tion of  green  plants  2.  Hibernation  and  aestivation,  p.  376.. 
3.   Local  distribution  of  animals,  p.  378.     4.   Pond  life,  p. 

385- 
II.    Adjustment  in  Manner  of  Life,  p.  390.      i.   Symbiosis,  p. 

390.  2.  Parasitism,  p.  396.  3.  Pollen  distribution,  p.  400. 
III.  Adjustment  in  Form  and  Appearance,  p.  404.  i.  The  re- 
adaptation  of  insects  to  aquatic  life,  p.  407.  2.  Phylogenetic 
adaptation  in  diving  beetles,  p.  415.  3.  Animal  coloration, 
p.  422. 

PRACTICAL   EXERCISES. 
Study  45.     Woodland  plant  society,  p.  373. 

Study  46.    Observations  on  the  dessication  and  resuscitation  of  rotifers, 
P-  378. 


CONTENTS  xiii 

Study  47.     The  local  resident  terrestrial  vertebrate  fauna,  p.  j8j. 
Study  48.    A  laboratory  examination  of  typical  pond  animals,  p.  j86. 
Study  4g.    A  field  study  of  pond  animals,  p.  j88. 
Study  §0.     The  relations  of  fungus  and  alga  in  the  lichen,  p.  JQ4. 
Study  §1.    A  comparative  examination  of  a  series  of  adult  parasites,  of 

a  single  order,  p.  400. 
Study  §2.    Pollen  production  as  affected  by  its  jnode  of  distribution,  p. 

402. 
Study  ^j.     The  principal  types  of  gills  found  in  aquatic  insects,  p.  410. 
Study  §4.     The  cornparative  development  of  respiratory  apparatus  in 

aquatic  inesct  larvae,  p.  41  j. 
Study  ^^.    A  comparison  of  the  structure  of  ground  beetle  and  diving 

beetle,  p.  417. 
Study  §6.    A  comparative  study  of  the  size  and  activities  of  diving 

beetles,  p.  418. 
Study  §1.    Field  observations  on  diving  beetles,. p.  420. 
Study  §8.     The  adaptive  structures  of  diving  beetles,  p.  421. 
Study  5p.    Examples  from  the  local  fauna  of  the  principal  types  of 

animal  coloration,  p.  432. 

CHAPTER  VII. 
THE  RESPONSIVE  LIFE  OF  ORGANISMS. 

Introduction,  p.  434. 
I.  Animal  Activities,  p.  437.  i.  Some  typical  sensory  phe- 
nomena of  the  Protozoza,  p.  437.  Organs  of  out-reach,  p. 
438.  Some  reactions  of  Paramoecium,  p.  439.  2.  Some 
general  features  of  the  sensory  mechanism  in  the  Metazoa,  p. 
441.  Intercommunication  without  nerves,  p.  442.  Sense 
organs  p.  444.  Nerve  and  muscle,  p.  448.  The  reflex 
arc,  p.  450.  Control  circuits,  p.  453.  Cephalisation,  p.  455. 
A  mechanism  for  adaptation  of  the  individual,  p.  457.  Re- 
lations between  parts  and  functions  in  the  vertebrates  p. 
460.  3.  Some  typical  sensory  phenomena  of  the  Metazoa, 
p.  469.  Automatic  unvarying  activities,  p.  469.  Respon- 
ses automatically  varying,  p.  469.  Sequences  of  automatic 
activities,  p.  473.  Learning  by  experience,  p.  479. 
II.  The  Responsive  Life  of  Man,  p.  485.  i.  The  natural 
history  of  man, -p.  48^.  Distinguishing  human  character- 
istics, p.  486.  Language,  p.  489.  Tool  using,  p.  490.  Use 
of  fire,  p.  491.     2.     Unwritten  human  history,  p.  492.     Ar- 


xiv  GENERAL  BIOLOGY 

chaeology,  p.  498.  Ethnology,  p.  494.  Ontogeny,  p.  498. 
3.  The  social  organism,  p.  500.  Animism,  p.  502.  Social 
integration,  p.  507.     Social  conduct,  p.  509. 

PRACTICAL   EXERCISES. 

Study  60.    Demonstration    of  functions  of  sonic  of  the  principal  parts 
of  the  nervous  system  in  the  frog,  p.  456. 

Study  61.  Observations  on  certain  activities  of  caterpillars,  p.  472. 

Study  62.  The  case-building  instincts  of  caddis  worms,  p.  477. 

Study  6 J.  Experiments  with  trial  and  error  in  chicks,  p.  481. 

Study  64.  Survivals  of  animism  in  our  own  titnes,  p.  504. 

APPENDIX. 

Preliminary  outline  and  instructions,  p.  513.  Lenses,  lighting, 
etc.,  p.  513.  Stage  mounts,  p.  518.  Dissecting,  p.  519.  Draw- 
ings, p.  520.  2.  Materials  for  the  practical  exercises,  p.  520.  3. 
Key  to  the  genera  of  Dytiscidce .     p.  526. 

INDEX. 

Pages  531—542. 


PORTRAITS:  Schultze,  p.  8g;  Pasteur,  p.  gT,;  Von  Baer,  p.  i'j4; 
Linnaeus,  p.  220;  Agassiz,  p.  224;  Darwin,  p.  277;  Leeuwenhoek,  p. 
298;   Mendel,  p.  309;  Aristotle,  p.  470. 


ru 


GENERAL  BIOLOGY 

CHAPTER  I. 
INTERDEPENDENCE  OF  ORGANISMS 

The  primary  demand  of  individual  livelihood  is  for  food. 
Getting  a  living  is  the  first  business  of  life,  and  food  is  the 
basis  of  a  living;  for  the  body  derives  both  its  substance 
and  its  energy  from  its  food. 

The  gathering  of  the  food  for  the  living  world  is  mainly 
the  work  of  green  plants.  These  derive  carbon  from  the 
air  and  mineral  matters  from  the  soil,  and  build  them  up 
into  living  substance,  clothing  the  earth  with  verdure  and 
storing  up  food  materials  that  make  animal  life  possible. 
Green  plants  constitute  in  themselves  by  far  the  greater 
part  of  the  living  substance  that  is  in  the  earth,  and  support 
other  forms  of  life  out  of  the  excess  of  their  product  over 
what  is  necessary  to  maintain  their  own  growth  and 
reproduction. 

The  primary  food  of  animals  is  plants  and  plant  products. 
Animals  consume  a  small  part  of  living  plants,  a  much 
larger  part  of  plant  products  (fruits,  tubers,  wood,  etc.) 
and  nearly  the  whole  of  plant  remains.  They  use  this 
plant  material  for  building  their  own  bodies  and  supplying 
their  energy,  and  excrete  it  again  as  simple  mineral  com- 
pounds. Thus  they  rapidly  restore  to  the  soil  plant  food 
materials  which  might  otherwise  remain  long  locked  up  in 
the  bodies  of  dead  plants.  Thus  the  world's  available 
supply  of  food  material  is  kept  in  circulation;  and  thus,  green 
plants  and  animals  are  complemental,  each  preparing  food 
for  the  other. 

That  so  large  a  part  of  living  vegetation  escapes  being 
eaten  is  due  to  the  fact  ^nat  animals,  primarily  herbivorous, 


4  GENERAL   BIOLOGY 

have  become  carnivorous,  and  have  taken  to  eating  each 
other.  The  carnivores  prevent  overproduction  of  herbivores, 
and  are  themselves  held  in  check  by  parasites  within  their 
own  ranks.  Herbivores  and  carnivores,  parasites  and 
scavengers  are  everywhere;  for  they  fulfill  permanent 
functions  of  animal  society. 

The  need  of  shelter  is  another  large  factor  in  determining 
the  habits  of  animals,  for  few  can  afford  to  live  in  the  open, 
and  most  are  so  limited  that  they  must  find  food  and 
shelter  in  the  same  haunts.  For  both  food  and  shelter 
animals  are  dependent  primarily  upon  plants  and  secondarily 
upon  each  other,  and  the  relations  that  have  come  to  exist 
between  them  are  so  intricate  they  may  fairly  be  compared 
to  a  web  with  its  threads  all  interwoven. 

Interdependence. — The  weak  are  dependent  on  a  few, 
the  strong  upon  many.  The  sturdy  oak  in  the  woods 
seems  very  independent  in  comparison  with  the  vine  that 
hangs  upon  its  branches  or  the  green  mould  lodged  in  a 
crevice  of  its  bark.  But  from  leaf  to  root  it  is  beset  by 
enemies  and  aided  by  friends.-  There  are  caterpillars 
feeding  upon  and  within  its  leaves.  On  its  twigs  are  aphids 
sucking  the  sap  out,  and  within  them  are  beetles  boring. 
Other  beetles  and  caterpillars  li\'e  in  bark  and  sapwood  and 
heartwood  of  its  trunk,  and  other  aphids  attack  its  roots. 

But  about  its  roots  there  are  friendly  earthworms  work- 
ing in  the  soil,  mixing  it  and  making  it  porous;  and  moulds, 
assisting  in  the  preparation  of  its  food.  Neighboring 
trees  shade  its  trunk  from  the  scorching  rays  of  the  summer 
sun,  and  woodpeckers,  nuthatches  and  warblers  search  its 
bark  and  leaves  for  hidden  insect  enemies.  There  are 
hosts  of  parasites  also,  individually  insignificant,  but 
collectively,  its  greatest  safeguards,  that  work  wholesale 


*In  Packard's  Forest  Insects  there  are  listed  442  species  of 
insects  affecting  American  oaks,  and  20  additional  that  are  found 
in  their  dead  stumps. 


INTERDEPEXDEXCE   OF  ORGANISMS  5 

destruction  upon  any  of  its  enemies  that  may  become 
excessively  abundant ;  and  even  the  squirrels  that  greedily 
gather  its  acorns  to  eat,  distribute  some  of  them  in  just  the 
way  to  insure  another  generation  of  oaks. 

Moreover,  this  complex  relation  began  at  its  birth,  and 
will  continue  until  it  is  "resolved  to  earth  again."  Weevils 
devour  its  acorns;  cutworms  and  lusty  smothering  weeds 
imperil  its  infancy;  and  the  trampling  and  browsing  of 
quadrupeds  are  a  great  menace  to  its  early  youth.  The 
storm  that  scars  it,  or  the  disease  that  weakens  it  m.akes 
the  opportunity  for  attack  by  beetles  or  molds  that  are 
harmless  in  its  health.  When  it  is  dead,  its  corpse  is 
riddled  by  borers  and  softened  by  molds  and  speedily 
reduced  to  dust. 

And  of  the  host  of  friends  and  enemies  with  which  it  has 
come  in  contact,  each  has  its  own  friends  and  enemies, 
ready  to  help  or  to  devour.  There  is  no  living  thing  that 
either  lives  or  dies  unto  itself  alone. 

Let  anyone  who  would  see  for  himself  the  complexity 
of  the  web  of  life,  study  some  common  plant  or  animal, 
observing  all  the  other  plants  and  animals  affect irg  it, 
and  their  inter-relationships ;  or,  let  him  examme  the  home 
of  some  social  animal,  and  find  all  the  inmates  of  different 
species,  and  learn  how  '  they  manage  to  live  together. 
There  is  no  plant  or  animal,  no  flower  or  fruit,  no  nest  or 
burrow,  no  carcass  or  log,  no  product  whatsoever  of  living 
nature,  that  will  not  show  a  community  of  life  with  re- 
lations infinitely  varied  and  complex.  To  see  how  much 
we  ourselves  are  continually  dependent  on  the  organic  life 
of  the  world,  we  need  only  examine  the  food  on  our  table, 
the  furnishings  of  our  house  or  the  materials  of  our  ward- 
robe; however  simple  these  departments  of  our  living  may  I 
be,  each  will  attest  that  many  kinds  of  plants  and  animals " 
from  many  parts  of  the  earth  are  tributary  to  it. 


GENERAL   BIOLOGY 


Balance  in  Nature. — To  the  careful  observer  the  face  of 
nature  changes  little  from,  decade  to  decade.  There  are 
giants  and  weaklings  in  every  natural  community,  but 
every  species  is  strong  enough  to  keep  on  living.  There 
are  shifts  of  place,  but  rarely  is  one  lost  in  the  shifting. 
Casualties  may  devastate  a  valley  or  a  hill  slope,  but,  left 
to  itself,  it  is  soon  repopulated. 

And   there  is  order  and  progress  in  the  shifting.     The 

fungi  growing 
on  this  stump 
(fig.  i)  and  the 
beetles  boring  in- 
side it,  are  not 
the  same  species 
that  will  feed 
there  when  it  is 
half  rotted;  nor 
is  any  one  of 
these  the  same 
thatw^ll  mix  its 
disintegrating 
fragments  with 
the  soil.  There 
will  be  other 
stumps  with  sound  wood  in  them  waiting  for  the  descend- 
ents  of  those  now  at  work  on  this  one.  The  conditions  for 
the  life  of  all  are  fairly  constant,  and  all  are  capable  of 
making  such  shifts  as  these  conditions  demand.  The 
balance  is  maintained  by  limitations  of  food  and  shelter 
and  increase  of  enemies,  serving  to  prevent  the  undue 
multiplication  of  any  species. 

Man  is  the  only  disturber  of  the  natural  balance  of  any 
consequence.  He  plows  under  the  mixed  population  of  the 
prairie  and  gives  the  soil  all  over  to  corn.     He  finds  the 


Fig.    1.      Oak  stump  in  an  early  stage  of  decay; 
shelf  fungi  on  the  bark. 


INTERDEPENDENCE   OF  ORGANISMS  7 

potato  a  wild,  straggling,  solitary  weed  in  the  hills  and 
propagates  it  and  covers  whole  acres  with  it.  Thus  he 
disturbs  the  balance,  for  the  enemies  of  the  com  and 
potato,  with  food  supply  enormously  increased,  multiply 
and  spread  as  never  before;  and  to  maintain  his  artificial 
conditions  man  must  continually  put  forth  his  hand  to 
assist  his  chosen  species  and  to  stay  their  enemies.  A  fev/ 
species  (such  as  the  bison  and  the  auk)  he  may  by  persistent 
slaughter  exterminate;  a  few  (such  as  cockroaches  and 
some  weeds)  multiply  in  spite  of  his  efforts  against  them; 
but  most  are  merely  held  in  check,  and  when  his  efforts 
against  them  cease,  they  speedily  reoccupy  their  former 
place. 

All  economic  procedure  that  deals  with  plants  and 
animals  is  based  upon  the  knowledge  of  their  relations  to 
each  other.  The  arts  that  feed  and  clothe  the  human 
race  make  progress  as  such  knowledge  is  advanced. 

It  is  the  purpose  of  the  studies  of  this  chapter  to  give  a 
closer  acquaintance  with  some  common  phenomena  il- 
lustrating close  interdependence  and  intricate  vital  relations 
between  organisms.  Three  subjects  have  been  selected  as 
especially  available  and  serviceable  to  this  end: 

1.  The  relations  between  flowers  and  insects. 

2.  Galls. 

3.  The  relations  between  ants  and  aphids. 

THE  RELATIONS  BETWEEN  FLOWERS  AND  INSECTS. 

Inter-relations  of  mutual  advantage  are  excellently 
shown  by  flowers  and  insects,  and  may  be  studied  anywhere 
during  the  flowering  season.  The  more  abundant  the 
flowers,  and  the  more  sunshiny  the  weather,  the  better  will 
be  the  opportunities.  Two  products  of  the  flowers  are 
eagerly  sought  by  insects  for  food,  nectar  and  pollen: 
Nectar  is  the  sugary  sap  of  the  plant  secreted  by  nectaries 


8  GENERAL   BIOLOGY 

that  are  generally  located  within  the  flower,  and  pollen  is 
the  product  of  the  stamens.  In  return  for  these  the  in- 
sects serve  the  flowers  by  transferring  the  pollen  of  one 
flower  to  the  stigma  of  another,  securing  cross  fertiliza- 
tion. 


Fig  2.  A  bee  {Macropis  ciliala)  gathering  pollen  from 
the  erect  stamens  of  a  loosestrife  flower  (Steironema 
ciliatum.) 

Figure  2  illustrates  this  relation.  The  yellow  flowers 
of  the  fringed  loosestrife  are  not  nectar-bearing  but  they 
produce  abundant  pollen.  This  is  much  sought  for  by  a 
little  black  bee.  The  bee  settles  upon  the  tops  of  the  clus- 
tered and  protruding  stamens,  as  shown  in  the  figure,  and 
scrapes  the  pollen  out  of  the  pollen  cavities  of  the  five  long 
curved  anthers.  In  doing  this  it  turns  around  several 
times  and  gets  the  hair  of  its  legs  and  of  the  under  surface 
of  its  body  filled  with  closely  packed  pollen  grains.  It 
visits  a  number  of  flowers  in  succession,  and  is  very  likely 
to  deposit  upon  the  stigma  of  each  one,  some  pollen 
from  another  flower. 

It  must  be  borne  in  mind  that  the  purpose  of  the 
flower  is  to  produce  seed.  Seeds  are  ripened  ovules:  ovules 
are    contained   in  the    ovule  case,    which    is  the     swollen 


INTERDEPENDENCE   OF  ORGANISMS 


and  hollow  base  of  the  pistil  (see  fig.  3).  This  central 
organ  is  the  most  important  part  of  the  flower  and 
all  the  other  parts  are  merely  accessory  to  its  seed  pro- 
ducing function.  A  slender  style  rising  from  the  top 
of  the  ovule  case  serves  to  hold  aloft  the  stigma  in  a 
proper  position  for  the  reception  of  pollen.  The  stigma  is 
the  moist,  uncovered  spot  on  the  tip,  where  the  tissues  of 
the  interior   are  exposed.     Pollen  grains  lodge  there,  and 

each  one  sends  out  along,  hollow  and 
excessively  slender  tubular  process 
(the  pollen  tube),  which  grows  down- 
ward through  the  tissues  of  the  style 
like  a  root  through  soil,  until  it  reaches 
an  ovule.  Fertilization  consists  in  the 
fusion  of  part  of  the  substance  that 
passes  down  the  pollen  tube  with  that 
contained  in  the  ovule,  and  will  be 
studied  in  a  subsequent  chapter. 
Suffice  it  to  say  here,  that  fertilization 
^'Sans of'^Sfe'wtJnfo  is  ncccssary  for  the  development  of 
fiJTanthe^r'; /"'filament;  ^ccd ;  and  that,  in  the  case  of  most  of 
wJi"^.  ^IfZ^llt"".  the  floAvers  that  are  visited  by  insects, 
?hV^bas'es''^of^^thr  fiia-  ^^  is  ncccssary  that  pollen  be  brought 
ThriotfeStoeVinXaTi  to  a  flowcr  from  the  flowcrs  of  another 
IndstTgmfatt°hlopI^-  pl^nt  of  the  samc  species.  This  is 
ing  of  the  flower.         .  cross-poUinatiou. 

In  the  loosestrife  there  are  five  stamens  arranged  in  a 
whorl  around  the  pistil.  Each  consists  of  a  large  curved 
pollen-bearing  anther  supported  on  a  long,  erect  filament. 
The  other,  accessory  parts  of  the  flower  (petals,  sepals,  etc.) 
while  wholly  unnecessary  to  seed  production,  are  often  of 
great  aid  in  vSecuring  cross-pollination,  being  often  wonder- 
fully adapted  to  suit  the  convenience  and  to  secure  the  aid 
of  insects. 


^^  - 


lO 


GENERAL   BIOLOGY 


See  how  the  loosestrife  flower  is  adapted  to  small  pollen 
eating  bees.  Its  stamens  stand  erect  with  anthers  curving 
inward.  The  trough-like  pollen  cavities  of  the  anthers, 
opening  upwa.rd,  expose  their  stores  to  the  insect  standing 
on  the  top.  So  great  is  the  excess  of  pollen  production  over 
actual  needs  that  the  little  the  bee  wastefully  and  unwit- 
tingly scatters  over  the  stigma  is  enough  for  setting  the 
seed.  This  store  of  choice  food  the  flower  reserves  for  its 
proper  visitors — chiefly  for  this  little  bee.  Large  bees 
would  have  great  difficulty  in  collecting  pollen  from  flowers 
that  hang  on  such  slender  stalks.  Wingless  insects,  like 
ants,  which,  if  gathering  pollen,  could  run  only  from  flower 
to  flower  upon  the  same  plant,  and  which  would  thus  be 
poor  agents  in  cross-pollination,  are  rigidly  excluded.  Should 
they  be  able  to  run  out  along  the  slender  flower  stalk,  and 
round  the  fringed  border  of  the  corolla  and  get  inside  it,  they 
would  still  find  between  themselves  and  the  pollen  overhead 
a  barrier  of  glandular  hairs  bearing  an  acrid  and  offensive  se- 
cretion with  which  they  would  choose  to  avoid  contact. 
This  flower  has  a"  simple  and  very  common  device  for 

preventing  self  pollin- 
ation. Its  anthers  ma- 
ture in  advance  of  its 
stigma.  When  the  flower 
opens  the  stigma  is 
turned  aside  (in  the 
position  indicated  by  the 
dotted  lines  in  fig.  3) ,  but 
later,  usually  when  its 
own  pollen  is  removed, 
the  stigma  is  lifted  up  into  the  proper  position  for  receiving 
that  brought  by  some  late  visitor  from  another  flower. 

This  simple  illustration  of  the  more  general  phenomena 
will  serve  to  introduce  the  following  studies  of  the  subject. 


Fig.  4.  The  flowers  of  a  willow  (Salix  dis- 
color.) r,  a  single  pistillate  flower,  removed 
from  its  cluster;  x,  its  covering  scale; 
n,  nectarv',  s,  section  of  its  ovule  case;/, 
clusters  (catkins)  of  staminate  flowers; 
u  and  V,  single  staminate  flowers  re- 
moved from  the  cluster. 


INTERDEPENDENCE  OF  ORGANISMS 


II 


Pig.  5.  Diagram  of  the  flower  of 
a  buttercup  (Ranunculus),  m, 
petal;  n,  nectary  on  the  base 
of  the  lowermost  petal;  o,  a  se- 
pal ■,p,  a  central  group  of  separate 
pistils;  q,  a  mature,  and  r,  an 
immature  anther. 


I.     The  adaptations  of  flowers  to    visitation  by  insects. 

Most  flowers  that  profit  by 
insect  visitation  are  composed  of 
the  four  whorls  of  organs  seen  in 
the  loosestrife  flower.  Two  of 
these  sorts  of  organs,  the  stamens 
and  the  pistils  are  essential  to 
seed  production :  the  other  two 
sorts,  petals  and  sepals  (the  floral 
envelopes  or  perianth)  are  merely 
accessory:  they  are  often  highly 
serviceable,  being  adapted  in 
manifold  ways  to  secure  the  visi- 
tation of  proper  insects.  These 
may  be  wholly  absent:  and 
stamens  and  pistils  may  be  de- 
veloped in  difi^erent  flowers,  or  even  upon  difl^erent  plants, 
as  in  the  willows  (fig.  4) . 

The  type  to  which  most  insect-visited  flowers  conform 
finds  a  simple  expression  in  such  a  flower  as  that  of  the  but- 
tercup (fig.  5).  There  are  many  separate  pistils  and  sta- 
mens: petals  and  sepals  are  separate  also,  and  alternate 
in  position:  all  the  parts  of  these  whorls  are  inserted  on  a 
common  receptacle  at  a  common  level:  the  nectar,  secreted 
under  a  little  scale  upon  the  base  of  each  petal,  is  quite  ex- 
posed and  readily  accessible  to  almost  all  visitors ;  and  the 
color    is  nearly    uniformly  yellow. 

These  characters  are  variously  modified  in  adaptation 
to  insect   visitors: 

a)  The  flowers  may  become  more  showily  colored  and 
more  attractive  to  the  eye.  They  may  be  specially 
marked  with  darker  or  lighter  streaks  or  blotches  about 
the  entrance,  as  if  to  guide  their  visitors  to  the  right 
place.     In     the  iris     (fig.    6)    there     are     three     separate 


12 


GENERAL  BIOLOGY 


U 


^ 


entrances,   each  with  its  own   guide   streaks:    and   at  the 
center  of  the  flower  where  there  is  no  entrance  there  is  a 

convergence    of  Hnes 
"^^  '  """^      that    often     deceives 

:  .  ill-adapted  visitors  in 

I  quest  of   the    nectar. 

Not  all  the  markings 
upon  flowers  are  thus 
significant:  doubtless 
the  deposition  of  pig- 
ment follows  struc- 
tural lines  and  results 
from  physiological 
causes,  and  may  often 
be  wholly  unrelated  to 
the  exigencies  of  pol- 
len transference.  But 
there  is  no  mistaking 
the  meaning  of  the  general  fact  that  flowers  adapted  to 
insect  visitation  are  showy,  while  flowers  whose  pollen  is 
distributed  by  wind  are  generally  inconspicuous;  or,  the 
fact  that  humming- 
bird flowers  are  scar- 
let; or,  that  night 
blooming  flowers  are 
oftenmost  white:  or, 
that  the  points  of  en- 
trance for  visitors  are 
conspicuously  mark- 
ed. 

b)   The  nectar     ex- 
hales a  great  variety 

of  attractive  scents,  and  the   nectaries  are    sequestered    in 
various  ways  beyond  the  reach    of    ill-adapted    visitors — 


Fig.  6.     Top  view  of  the  flower  of  a  wild  iris 
{Iris  versicolor). 


Fig.  7.  Diagrams  of  forms  of  corollas,  a,  bell- 
form;  b,  funnel-form;  c,  tubular;  d,  spurred; 
e,  two-lipped;  a,  b,  c  are  radial;  d  c^nd  e, 
bilateral. 


INTERDEPEXDEXCE   OF  ORGANISMS 


13 


hedged  about  with  spines  or  glandular  hairs,  or  hidden 
at  the  bottom  of  deep  or  closed  passageways — and  thus 
reserved   for  the   use  of  proper  guests. 

c)  The  floral  organs  may  become  grown  together 
in  various  ways.  This  tendency  toward  fusion  of 
parts  is  strongest  among  the  pistils  and  the  petals.  In  the 
loosestrife  flower  (fig.  3)  all  the  petals  and  stamens  are 
grown  together  at  the  base.  This  stiffens  the  flower,  and 
makes  it  better  able  to  support  the  trampling  of  a  visiting 

insect.  Often  the  fu- 
sion of  parts  is  of  great 
importance  in  se- 
questering nectar  (fig. 
21)  and  forming  the 
passageways  thereto. 
This  is  the  meaning  of 
the  various  forms  of 
corollas,  the  principal 
types  of  which  are 
shown  in  the  accom- 
panying diagram  (fig.  7). 

d)  The  parts  may  become  unlike  in  each  whorl,  making 
the  flowers  irregular:   or 

e)  They  may  lose  their  symmetrical  arrangement,  and  no 
longer  alternate  regularly  in  each  whorl:   or, 

f)  Some  of  the  parts  may  be  lost  through  atrophy:  or 

g)  The  flower  may  cease  to  be  radial  and  become  bilateral. 
This  point  is  the  concomitant  of  the  three  preceding.  Bi- 
lateral flowers  show  the  completest  structural  adaptations 
to  insect  visitors.  They  generally  face  laterally,  and  are  so 
shaped  that  the  insect  enters  in  one  position  only.  The 
corolla  is  usually  two-lipped,  with  the  lower  lip  serving  as  an 
alighting  place,  and  the  upper  as  a  shelter  for  the  pollen 
(fig.  8).     The  stamens  are  often  reduced  to  one  or  two  pairs, 


Fig.  8.     Typical  bilabiate  flowers  of  Prunella 
(P.  vulgaris  L.) 


14 


GENERAL   BIOLOGY 


-/.4C 


1-^ 


\ 


a 


"[  4'   ^/   V  <il  i> 


and  the  anthers  are  so  situated  that  the  insect  rubs  against 
them  at  just  the  right  time,  entering  or  leaving :  in  this  con- 
sist some  of 
the  most  won- 
derful exam- 
ples of  adjust- 
ment. 

It  is  one  of 
the  delights  of 
the  student  of 
floral  struc- 
tures to  trace 


Fig  9.  Diagram  of  types  of  flower  cluster,  a,  panicle; 
h,  raceme;  c,  spike;  cf,  spike  contracted  to  heatl; 
e,  corymb;  /,  head;  g,  umbel;  h,  cyme. 


these  organs 
through  all  their  modification  of  form,  position  and  arrange- 
ment, and  to  be  able  to  recognize  them  under  all  their  dis- 
guises. 

The  flower  cluster. — Two  important  ends  seem  to  be 
served  by  the  close  grouping  of  flowers  together  in  clusters, 
i)  vShowiness  is  secured  w^ith  much  less  expenditure  of  vital 
energy  in  the  production  of  sterile  parts.  The  single  flower 
of  the  common  elder  is  very  small  and  insignificant,  but  the 
big  flat-topped  clusters  of  elder  flowers  are  borne  aloft  upon 
the  clumps,  in  such  a  way  that  they  may  readily  be  seen 
from  afar  off:  2)  The  bringing  of  the  flowers  together  in 
compact  clusters  makes  it  possible  for  the  insect  to  pass 
from  one  flower  to  another  Avithout  taking  flight.  This 
greatly  economizes  labor  for  the  insect.  The  principal 
forms  of  flower  cluster  are  shown  in  the  accompanying 
diagram  (fig.  9).  It  will  be  seen  that  with  respect  to 
compactness  and  rigidity,  improvements  in  arrangement 
culminate  in  flat-topped  heads. 

Study  I.     Flowers  adapted  to  insect  visitation. 
Apparatus  needed :     A  lens  and  a  forceps. 


INTERDEPENDENCE   OF  ORGANISMS  15 

Materials  needed :  Flowers  of  ten  or  more  species  (pref- 
erably native) ,  in  sufficient  abundance  so  that  all  stages  of 
flowering  from  the  bud  to  withering  can  be  found.  They 
must  be  fresh:  if  wilted  when  brought  in,  they  may  be  re- 
vived by  being  placed  under  a  bell  jar  with  water  for  a  time. 

The  student  will  need  so  to  familiarize  himself  with  the 
parts  of  the  flower  as  to  be  able  to  recognize  them  under  all 
their  disguises.  Whatever  their  form  the  pollen-bearing 
parts  are  the  stamens,  and  the  stigmatic  surface  is  upon  the 
pistil.  These  parts  should  be  examined  at  first  in  fresh, 
full  blown,  and  old  flowers  of  some  species  of  good  size  in 
order  to  determine  the  appearance  of  anther  and  stigma  at 
maturity.  And  the  nectaries,  which  are  in  appearance 
often  hardly  more  than  pellucid  spots  of  greenish  tissue  with 
minute  droplets  of  nectar  exuding  from  them,  should  at 
the  first  be  distinctly  recognized.  The  commoner  forms  of 
corolla  and  of  flower  cluster  should  be  learned.  The  fore- 
going figures  may  be  supplemented  by  those  in  any  good 
text  book  of  botany. 

Tabulation  of  observations. — A  sheet  of  paper  ruled  in 
tabular  form  should  be  prepared  with  the  following  column 
headings  (abbreviated  as  desired) : 

Nam.e  of  plant. 

Order  (or  family)  to  which  it  belongs. 

Form  of  flower  cluster  (fig.  9). 

Parts  of  flower  that  are  colored  (white  is  a  color,  and 
green  is  not,  in  botany). 

What  colors. 

"Guide  marks,"  indicating  the  entrance  to  the  nectaries. 

Odor,  its  strength,  character,  etc. 
fform  (fig.   7). 

Corolla  J  symmetry,  (radial  or  bilate^-al) . 
I  open  or  closed. 


1 6  GEXERAL   BIOLOGY 

Guards  against  waste  of  nectar  by  rain. 

Guards  against  the  ingress  of  ill-adapted  \'isitors. 

Position  of  the  nectaries. 

f  number. 
Stamens    ^  arrangement  (in  pairs,  in  whorls,  etc.) 

[  included  or  exserted. 
Pollen  (dry,  sticky,  etc.) 
Guards  against    self-  )     [  structure, 
fertilization      in   >  ^  position , 
stigma  or  anther  )     |^  movements. 
First  ready  for  fertilization,  anther  or  stigma. 

The  student  will  use  this  table  for  recording  his  observa- 
tions on  the  ten  or  more  species  of  flowers  selected,  which 
should  include  the  following  floral  types: 

1.  K  simple  open  solitary  flower. 

2.  A  tubular  or  bellshaped,  loosely  clustered  flower. 

3.  A  spurred  or  saccate  flower. 

4.  A  strongly  bilateral  mint  flower. 

5.  A  papilionaceous  flower. 

6.  An  umbelliferous  flower. 

7.  A  malvaceous  flower. 

8.  A  composite  flower   (see  fig.   236.) 

Interpretation  of  the  table. — The  student  should  write  out 
the  principal  conclusions  that  can  be  drawn  from  the  facts 
included  in  the  completed  table.  In  doing  this  he  should 
consider  the  facts  of  each  column  by  themselves,  and  after- 
wards, looking  for  correlated  characters,  he  should  compare 
the  columns  together.  For  example,  he  will  be  able  to  see 
in  the  several  columns  what  forms  of  flowers  cluster  and  of 
corolla;  what  colors,  guide-marks,  scents;  what  rain  guards, 
etc.  prevail:  but  it  is  only  by  carefully  comparing  columns 
together  he  will  learn  which  of  the  flowers  show  fewest 
adaptations  to  insect  visitors,  which  of  the  tubular  and 
which  of  the  bilateral  flowers  show  most    adaptations,  and 


INTERDEPENDENCE   OF  ORGANISMS 


17 


head 


thorax 


abdoMcn 


whether  there  exists  any  correlations  between  bilaterality, 
position  of  the  flower  in  the  cluster,  arrangement  of  the 
stamens,  etc. 

2.     The  adaptation  of  insects  to  flower  visitation. 

In  the  body  of  an  in- 
sect there  are  three  prin- 
cipal divisions:  head, 
thorax  and  abdomen. 
The  head  bears  eyes, 
antennae  and  mouth- 
parts,  the  latter  con- 
sisting of  upper  and 
lower  lips,  with  two 
pairs  of  jaws  working 
horizontally  between 
them. 


Fig.  10.  Diagram  of  the  externa]  parts  of  an 
insect,  a,  antennae;  £",  eye;  oc,  ocelli;  /,  pro- 
thorax;  //,  mesothorax;  ///,  metathorax; 
w,    and  Wo,   fore  and   hind  wings;   /j,   U,  /j, 


fore,  middle   and   hind   legs;  i, 
segments  of  the  abdomen. 


3,  4.  etc. 


The  thorax  is  di- 
vided into  three 
horny  rings  or  seg- 


of 

pair 

the 

two 


ments,      each 
which  bears  a 
of   legs,     and 
hindmost 
bear  each  a  pair  of 
wings.     The  abdo- 
men consists   of   a 
variable  number  of 
segments. 

The  accompany- 
ing diagram  (fig.  10) 

will  serve  to   repre-     pj(,    ^       Mouthparts  of  grasshopper  and  beetle,     a, 
„p„j.      ij-p      arrancrp-  ia.ce\[ie-woigras?,hopper{Melanoplus  femur-rubrum) 

ment   of    parts  for 
insects  in   general. 


showing  at  /,  labrum;  b,  labium  of  same;  c,  mandi- 
ble of  same;  d,  maxilla  of  same;  ^.mandible  of 
soldier  beetle  (C"/iaM/zogna</iz<5  scutellaris)  \  /.maxilla 
of  same,  showing  pollen  brushes. 


i8  GEXERAL   BIOLOGY 

Since  insects  visit  flowers  for  food,  naturally,  it  is  the  parts 
of  their  bodies  that  serve  for  collecting  and  carrying  the 
nectar  or  pollen  that  are  most  modified  for  flower  visitation. 
It  is  their  feeding  apparatus,  therefore,  that  most  merits  our 
present  attention.  The  nature  of  the  remarkable  changes 
that  have  fitted  insect  mouthparts  for  nectar-gathering  will 
best  be  understood  after  comparison  with  the  simple  biting 
mouthparts  of  a  grasshopper.  These  are  shown  in  fig.  ii. 
The  upper  lip  or  labrum  is  a  simple  transverse  membranous 
flap  covering  the  mouth  above.  The  lower  lip  or  labium  is 
a  compound,  appendage-bearing  flap  covering  the  mouth 
below.  Between  the  two  are  tAvo  pairs  of  jaws  that  swing  in 
and  out  laterally,  and  that  are  toothed  on  their  opposed  tips; 
but  one  of  each  pair  is  shown  in  the  figure.  The  upper  pair 
(mandibles)  lie  directly  beneath  the  labrum ;  each  mandible 
is  simple  and  strongly  toothed.  The  lower  pair  (maxillae) 
lie  directly  below  the  mandibles,  between  them  and  the 
labium.  Each  maxilla  consists  of  two  basal  pieces  {cardo 
and  stipes)  and  three  terminal  appendages;  the  innermost, 
the  lacinia,  is  simple,  and  toothed  internally;  the  next,  the 
galea,  is  two  jointed  and  closely  fits  over  the  back  of  the 
lacinia;  and  the  third,  the  palpus,  is  five  jointed  and  is 
sensitive  at  its  tip.  The  labium  is  a  compound  organ  made 
of  a  pair  of  appendages  similar  to  the  maxillae,  fused  to- 
gether during  their  development  on  the  middle  line.  The 
fused  cardines  constitute  the  submentum,  the  fused  stipites, 
the  mentum,  and  the  three  terminal  parts  are  easily  recog- 
nizable, although  the  lacinia  is  greatly  reduced  in  size,  the 
galea  greatty  expanded,  and  the  palpus  but  three  jointed. 

Of  insects  with  this  simple  type  of  mouthparts,  only  a  few^ 
chiefly  beetles,  have  taken  to  flower  visiting;  and  these 
show  more  or  less  of  narrowing  of  the  front  of  the  head, 
adapting  it  for  entering  corollas,  and  alteration  of  the  tip  of 
the  lacinia  to  brushes  of  stiff    pollen-,  or  nectar-gathering 


INTERDEPENDENCE   OF  ORGANISMS 


^9 


hairs,  in  place  of  the  usual  teeth.  This  is  shown  in  our  figure 
for  a  pollen-eating  soldier  beetle  {Chauliognathus  scuiellaris) 
which  swarms  upon  goldenrod  flowers  in  autumn  (fig.  ii.) 
Proboscides — Most  nectar-eating  insects  have  mouthparts 
prolonged  and  combined  into  some  sort  of  a  sucking  pro- 
boscis, with  which  they  are  better  able  to  reach  sequestered 
nectaries.  In  general  it  may  be  said  that  the  proboscides 
are  of  three  types: 

1.  The  hinged  and  retractile  type,  variously  developed 
in  bees  and  flies. 

2.  The  coiled  type,  characteristic  of  butterflies  and 
moths. 

3.  The  jointed  and  rigid  type,  characteristic  of  bugs 
(Hemiptera). 

The  first  of  these  types  is  well  illustrated  by  the  common 
honey  bee,  in  which  the  proboscis  is  made  out  of  m.axillae 
and  labium.  Labrum  and  mandibles  are  much  as  in  the 
grasshopper:  the  labrum  is  narrower,  and  the  mandibles 
are  not  toothed  at  the  tip,  but  scoop-like,  adapting  them 

for  moulding  wax.  But  the 
maxillae  and  the  labium  are  exces- 
sively elongated,  hollowed  out  in- 
ternally and  closely  applied  together 
to  form  a  sucking  tube,  the  anterior 
part  of  the  alimentary  canal  being 
at  the  same  time  modified  to  form  a 
sucking  organ  and  nectar  reservoir. 
The  resultant  proboscis  is  slung 
beneath  the  head  upon  the  car- 
dines  of  the  maxillae  (fig.  12  f),  and  provided  with  muscles 
which  readily  extend  or  retract  it.  At  the  tip  of  the  stipes 
is  another  hinge,  which  allows  the  long  terminal  portion  to 
be  folded  backward  under  the  head  when  not  in  use.  This 
terminal  composite  joint  is  hollow,  and  from   its  tip  pro- 


FiG.  12.  Diagram  of  head  of 
honey  bee  {Apis  niellifica, 
from  the  side,  a,  antenna; 
6,  eye;  c,  labrum;  d,  mandi- 
ble; e,  maxilla;  r,  its  cardo; 
s,  its  stipes  and  p,  its  palpus ; 
/,  labium,  p,  its  palpus. 


20 


GENERAL   BIOLOGY 


jects  a  long,  slender  hairy  tongue,  that  is  itself  retractile, 
and  that  bears  a  minute  membranous  nectar-lapping 
lobe  at  its  tip.  These  parts  seem  at  first  very  unlike 
labium  and  maxilla  of  the  grasshopper,  but  it  is  not 
difficult  by  separating  them  and  examining  them 
carefully  to  recognize  their  identity.  In  the  accompanying 
figure  (fig.  13)  the  parts  are  all  indicated  by  name;   and  the 

proboscis  of  a  short-tongued  bee  is 
similarly  drawn  and  lettered  to  make 
their  recognition  easier.  It  will  be  ob- 
served that  in  the  honey  bee  the  long, 
tubular  terminal  joint  of  the  proboscis 
is  composed  of  the  hollowed  out  laciniae 
of  the  maxillae  and  basal  segments  of 
the  labial  palpi,  closely  applied  together. 
In  the  flies  (Diptera)  labium  and 
mandibles  are  rudimentary,  the  rudi- 
ments of  the  maxillae  are  intimately 
combined  with  the  highly  specialized 
labium  to  form  the  proboscis,  which 
is  hollow,  retractile  beneath  the  head, 
its  terminal  joint  folding  downward, 
much  as  in  the  bees:  but  at  its  tip, 
instead  of  the  hairy,  decurving,  pro- 
trusible  tongue,  there  is  often  developed 
a  pair  of  up-folding,  opposible  flaps 
(labellae)  with  corrugated  inner  sur- 
faces (fig.  14).  Since  investigators  are 
not  wholly  agreed  as  to  the  identity  of 
parts  in  the  fly  labium,  it  will  be  suffi- 
cient if  the  student  note  its  length,  its 
folding  and  extension,  the  action  of  its  labellae,  and  other 
characters  that  have  to  do  with  pollen  and  nectar  gathering. 


Fig.  13.  Comparative 
diagrams  of  probos- 
cis of  long-tongued 
and  short-tongued 
bees.  Upper  figure, 
the  honey  bee 
(Apis).  Lower  fig- 
ure (Halictus,  from 
Dr.  W.  A.  Riley) ; 
a,  labrum;  b,  man- 
dibles; c,  maxillae; 
d,  labium ;  p,  pal- 
pus. 


INTERDEPENDENCE  OF  ORGANISMS 


21 


Fig.  T4.  Diagram  of  head  and  pro- 
boscis of  a  syrphus  fly  {Rhingia 
nasicd).  a.  antenna;  h,  eye:  c, 
proboscis,  with  parts  outspread; 
h,  its  hinge .  /  its  labellae. 


The     coiled     proboscis  of  moths  and   butterflies  is  the 
most  specialized  of  all,  and  limits  its  possessors  to  feeding  on 

liquids.  So  slender  as  to  be 
filiform,  coiling  compactly  like 
a  watch  spring  beneath  the 
head,  and  extending  when  un- 
rolled to  a  length  sometimes 
exceeding  the  length  of  the 
body,  it  is  adapted  for  reach- 
ing the  nectar  in  the  deepest 
corollas,  and  for  entering 
the  narrowest  passageways. 
Moreover,  it  is  most  unique 
in  structure  in  that  it  con- 
sists of  the  laciniae  of  the  two  maxillae  only,  these  be- 
ing elongated,  channelled  within  and  closely  applied 
together  to  form  a  tube.  The  only  other  mouthparts 
that  are  well  developed  in  the  commoner  butterflies  and 
moths  are  the  labial  palpi, 
which  project  forward  from 
beneath  the  head,  and  be- 
tween which  the  proboscis 
coils  itself  up  when  at  rest. 
So  greatly  have  the  mouth- 
parts  been  modified  that 
the  identity  of  them  in  their 
present  condition  would 
not  be  recognized  by  a 
beginner;  the  accompanying 
diagram  (fig  15),  of  a  speci- 
men cleaned  of  the  scales  which  densely  cover  the  ves- 
tigial organs,  indicates  all  the  parts  by  name. 

The  jointed  proboscis  of  the     Hemiptera    is    relatively 
unimportant  in  nectar   feeding.     It  is  rather    adapted   for 


Fig.  15.  Diagrams  of 
head  and  mouthparts 
of  a  butterfly  a, 
side  view  of  head, 
with  proboscis  partly 
uncoiled;  b,  oblique 
view  of  face,  denuded 
of  scales;  /,  labrum; 
md.  mandible  ;^,  rudi- 
mentary palpus  of 
maxilla;  x,  proboscis, 
composed  of  con- 
.loined  laciniae  of 
maxillae:  i,  labium, 
with  the  large  ter- 
minal joint  of  the 
proximal  palpus  re- 
moved. 


22 


GENERAL  BIOLOGY 


sap. 
Its 


piercing  the  tissues  of    plants    and    sucking    out  the 
Only  incidentally   is    it   used    for    gathering    nectar. 

very  position  and  direction  show  it  to  be 
unadapted  to  probing  flowers. 

It  consists  of  two  pairs  of  lancet-like 
org^ans,  the  modified  mandibles  and 
maxillae,  enveloped  by  the  sheathing 
lower  lip,  which  is  practically  destitute 
of  palpi,  and  distinctly  jointed:  the 
labrum  is  rudimentary.  The  accom- 
panying diagram  shows  the  parts  as  they 

somewhat     separated 


Fig.  16.  Diagram  of 
head  and  proboscis 
of  a  bug  {Pemato- 
ma).  a,  antenna; 
b,  eye;  c,  labrum; 
d,  lancet-like  man- 
dibles; e,  maxillae; 
/,  the  jointed  en- 
sheathing  labium . 

of    the     body. 


appear      when 

(fig.  1 6). 

Vesture. — 

The  parts  thus 
far  considered 
have  to  do  with 
getting      food. 

,Tf^  .-,-,  ,  Fig.  17.  Side  view  of  abdomen 

We      VAii    next  of  a    hee{  Macro  pis),  show - 

•J  -fVi    +  ^"S  ventral  pollen  brushes. 

which  has  to  do  with  the  distributing  of 

pollen,  the  vesture,    or   hairy  covering 

The    horny    shell    of    the    insect's     body 

if  bare  would  carry 
little  pollen,  but  the 
brushes  of  hairs 
with  which  it  is 
usually  clothed  carry 
pollen  excellently  and 
serve  well  for  mi- 
planting  some  of  it 
on  the  surface  of  the 
stiema. 


Fig.    18.     Pollen  gathering  hairs  of  the  honey  bee. 


IXTERDEPEXDEXCE  OF  ORGAXISMS 


23 


It  is  a  part  of  the  fitness  of  things 
that  these  brushes  are  usually  best  de- 
veloped on  the  top  of  the  thorax,  the 
under  surface  of  the  abdomen  (fig.  17) 
and  the  outer  faces  of  the  legs — the  places 
of  most  frequent  contact  with  anthers 
and  stigmas :  but  special  tufts  of  hair  or 
scales  are  occasionally  found  in  unusual 
places,  serving  the  needs  of  some  partic- 
ular flower.  The  hairs  of  many  bees 
and  syrphus  flies  bear  numerous  mi- 
croscopic lateral  branches  and  hold  pol- 
len grains  the  more  securely  in  the  angles 
of  the  branchlets  (fig.  18).  The  hairs 
may  gather  of  themselves  sufficient  pol- 
len to  be  worthy  of  consideration  as 
food:  but  the  pollen  must  then  be 
gathered  up  and  massed  together,  and  for  this  purpose 
"pollen  combs"  (fig.  19)  are  developed  upon  the  inner  face 
of  the  enormously  enlarged  basal  joint  of  the  hind  torsus 
of  bees,  and  a  "pollen  basket"  is  developed  on  the  outside 
of  each  hind  leg. 


Fig.  19.  Hind  leg  of 
bee,  ex,  coxa;  tr, 
trochanter;/,  femur 
I,  tibia;  i,  2,  3,  4,  5, 
segments  of  the 
tarsus;  i,  carrying 
the  "pollen  combs." 


Other  parts. — The  modifications  of  other  parts  of  the  in- 
sect, antennae,  wings  and  legs,  have  to  do  chiefly  with  ac- 
commodating it  to  entering  corollas.  Obviously  the  but- 
terfly shown  in  figure  20  could  not  enter,  and  does  not  need 
to  enter  bodily  into  a  flower.  The  bee  will  again  illustrate 
by  what  means  the  antennae  have  been  made  reversible, 
the  legs,  closely  applicable  to  the  sides  of  the  body,  and 
the  wings,  close-folding  upon  the  back;  the  whole  insect 
compacted  together,  and  admirably  fitted  for  getting  into, 
and  for  getting  out  again  from,  the  tight  places  on  the 
road  to  the  nectar  in  specialized  corollas. 


24 


GENERAL  BIOLOGY 


How  to  know  the  orders 
of  flower  insects. — But  five 
orders'"''  of  insects  are  com- 
monly found  upon  flowers. 
The  membersof  these  orders 
may  readily  be  recognized 
by  the  following  single 
distinctive  characters : 

The  Diptera  alone  have 
but  two  wings. 

The    Lepidoptera    alone 
have    the    wrings    covered 
with   dust-like   scales  that 
rub  off  between  the  thumb 
and     finger:      likewise,     a 
coiled  proboscis. 
The  Coleoptera  alone  have  the  fore  wings  {elytra)   meet- 
ing in  a  straight  line  down  the  middle  of  the  back,  not  over- 
lapping. 

The  Hemiptera  alone  have  a  jointed  proboscis  directed 
backward  between  the  fore  legs. 

The  Hymenoptera  alone  have  a  sting;  likewise,  they 
lack  all  the  preceding  characters:  the  small  hind  wings 
being  usually  attached  to  the  margin  of  the  fore  wings  by  a 
series  of  hooklets,  the  beginner  may  overlook  them  at  first. 

Study  2.     Insects  adapted  to  visiting  flowers. 

Apparatus  needed:  A  cyanide  bottle,  an  air  net  and  a 
lens. 

Materials  needed:  Ten  or  more  species  of  insects,  to  be 
gathered  from  flowers  by  the  student,  who  should  observe 


Fig.  20      Butterfly  {Colias  philodice)  on 
a  clover  head. 


*Omitting  from  consideration  the  minute  but  ever  present  thrips 
(order  Physopoda)  found  hidden  within  the  flowers — insects  usually 
less  than  a  millimeter  long,  with  straight  bodies  and  veinless  wings, 
of  slight  importance  in  this  connection. 


INTERDEPENDENCE  OF  ORGANISMS  25 

the  while  what  each  insect  is  doing,  in  order  to  be  able  to 
interpret  the  meaning  of  its  peculiarities  of  structure.  The 
advantage  of  possessing  elbowed  and  reversible  antennae, 
for  example,  can  only  be  appreciated  after  seeing  a  bee 
force  an  entrance  into  a  closed  corolla,  such  as  that  of 
Linaria  (fig.  169). 

The  insects  should  then  be  studied  in  the  laboratory,  not 
too  hastily,  and  while  still  fresh.  If  allowed  to  become 
brittle  through  drying,  they  may  be  relaxed  again  by  plac- 
ing in  a  moist  atmosphere  (as,  under  a  bell  jar  with  a  wet 
sponge)  for  a  few  hours. 

They  should  include  the  following  types: 
I.     A  long-tongued  bee  (bumblebee). 
A  short-tongued  bee. 
A  wasp. 

A  fly  (two  winged). 
A  beetle. 
A  bug. 
7.     A  butterfly  or  moth. 


The  record  of  observations  should  be  made  in 
a  table  prepared  with  the  following  column  headings  (ab- 
breviated as  desired) : 

Name  of  the  insect. 

Order  to  which  it  belongs. 

Flowers  on  which  it  was  taken. 

Seeking  pollen  or  nectar. 

Proboscis     l  -,         , 
\  length 

Pollen-gathering  parts. 

Antennae — length,  form  and  position. 

Position  of  wings  when  at  rest. 

Relative  size  and  weight  (as  compared  with  the  others 

of  the  table). 


26 


GEXERAL   BIOLOGY 


J- 


The  relative  fitness  of   the  different  visitors  to  one 

kind  of  flower. 

It  will  have  been  observed  in  the  course  of  the  field  studies 
hitherto  outlined,  that  not  all  the  visitors  to  one  kind  of 
flower  are  equally  proficient  in  obtaining  its  stores  or  in 

transferring  its  pollen:  also,  that 
the  manner  of  visitation  is  A^ery 
different  in  different  insects.  The 
butterfly  perching  atop  of  a  phlox 
corolla  and  probing  the  deep  tube 
only  with  its  long  proboscis  (fig.  21) 
could  not  exchange  places  with  the 
bee  that  plunges  bodily  into  the 
chelone  flower  (fig.  22):  it  would 
'^^^■^^-      Diagram  of  a  butter-  meet  with  difficulties  like  those  of 

flv  on  Phlox,  and  of  the  posi- 
tion of  the  stamens  within  the  stork  of  thc  fable,  attempting 

the  corolla  tube.  .  »  j-         o 

to  dine  with  the  wolf.  A  more 
careful  study  of  this  matter  will 
show  that  the  pollination  of  a 
flower  may  be  well  effected  by  in- 
sects that  operate  in  very  different 
ways. 

The  following  study  of  all  the 
visitors  to  one  kind  of  flower  is  in- 
tended to  reveal  the  actual  rela- 
tions existing  between  a  flower  and 
its  visitors,  and  the  relative  fitness 
of  these  visitors.  Clearly  this  fit- 
ness consists  in  two  things:  i) 
ability  to  get  the  food  store  the  flower  offers,  and  2)  ability 
to  transfer  pollen  from  anther  to  stigma. 

Study  J.     All  the  visitors  to  some  common  flower. 
Apparatus  needed:     insect  net,  cyanide  bottle,  lens  and 
note  book:   use  chiefly  the  two  last  mentioned. 


Fig.  22  The  flower  of  turtle 
heads  {Chelone  glabra),  and 
its  visitor  (worker  Bomhus). 


INTERDEPENDENCE   OF   ORGANISMS  27 

First,  select  a  flower  that  is  abundant,  and  that  has  pol- 
len and  nectar  so  exposed  as  to  be  accessible  to  a  consider- 
able variety  of  visitors.  Before  beginning  to  observe 
the  visitors  study  the  structure  of  the  flov/er  itself ,  as  to  i) 
the  position  of  the  pollen  and  nectar  stores,  2)  the 
passageway  to  the  nectar  and  its  guards,  3)  the  position 
of  anthers  and  stigmas  in  relation  to  this  passage  at 
different  stages  of  flo'vvering,  and  if  clustered,  4)  the  form  of 
cluster  as  likely  to  affect  the  convenience  of  big  or  little 
visitors. 

The  field  work  of  the  following  outline  must  of  necessity 
be  individual:  it  cannot  be  done  in  a  crowd:  the  student 
should  work  quite  alone  so  as  to  avoid  having  his  observa- 
tions interrupted  by  the  movement  of  companions.  He 
should  w^ear  quiet  colors,  and  approach  the  insects  cau- 
tiously, avoiding  quick  motions :  thus  it  will  be  quite  possible 
to  observe  many  of  them  at  work  under  a  lens.  Some 
degree  of  warmth  and  sunshine  and  dryness  of  the  weather 
will  also  be  necessary  to  success. 

The  record  of  observations. — From  a  study  of  as  many 
kinds  of  insect  visitors  as  can  conveniently  be  found,  fill 
out  a  table  prepared  with  the  following  column  headings 
(abbreviating  as  desired) : 

I.     Name  of  the  insect. 

Order  to  which  it  belon^'S. 

Seeking  pollen  or  nectar. 

Alights  where.  , 

Enters  how  far. 

Touches  stigma  or  anther  first. 

Carries  pollen  how. 

Visits  how  many  flowers  in  succession  without  inter- 
vening long  flight. 

9.     Visits  how  many  flowers  per  minute. 


28  GENERAL    BIOLOGY 

lo.  Well  or  ill-adapted  for  visiting  and  pollinating  this 
flower. 

4.     The  relative  fitness  of  the  different  flowers  visited  by  one 
kind  of  insect  to  profit  by  its  visitation. 

A  more  careful  study  should  now  be  made  of  the  relations 
existing  between  one  kind  of  insect  and  the  many  kinds  of 
flowers  it  visits.  This  is  a  study  of  the  relative  fitness  of 
the  several  flowers  to  avail  themselves  of  its  services  as  an 
agent  of  pollen  distribution.  Clearly  fitness  in  this  case 
consists  in  i)  oft'ering  the  insect  an  accessible  food  supply 
to  win  its  visits,  and  2)  having  anther  and  stigma  located 
aright  for  proper  pollen  transference. 

Study  4.     All  the  fiowers  visited  by  some  common  insect. 

Apparatus  needed  and  general  directions,  as  for  preceding 
study.  An  insect  should  be  selected  that  is  abundant,  that 
is  an  active  flower  visitor;  it  should  have  a  rather  long 
proboscis  in  order  that  it  may  have  access  to  flowers  of  con- 
siderable variety.  It  should  be  carefully  examined,  before 
the  proper  work  of  this  outline  is  undertaken,  as  to  i)  its  nec- 
tar-gathering parts,  particularly  as  to  the  length  and  posi- 
tion of  its  proboscis;  2)  the  position  and  structure  of  its 
pollen  brushes;  and  3)  its  size  and  weight,  and  4)  the  position 
of  its  appendages  when  at  rest. 

The  record  of  observations. — In  the  field  one  should  ex- 
amine freshly  blooming  clumps  of  as  many  kinds  of  flowers 
as  possible,  first  seeing  whether  the  insect  selected  for  study 
is  visiting  them,  and  if  so,  watching  it  carefully  and  quietly 
until  the  points  given  below  as  table  headings  have  been 
determined : 

1.  Name  of  flower. 

2.  Furnishes  pollen  or  nectar. 


INTERDEPENDENCE   OF  ORGANISMS  29 

3.  Offers  what  alighting  place. 

4.  Is  entered  how  far. 

5.  Stigma  or  anther  touched  first. 

6.  Pollen  carried  how. 

7 .  ■  Number  of  flowers  visited  in  succession  without  inter- 
vening long  flight. 

8.  Number  of  flowers  visited  per  minute. 

9.  Well  or  ill-adapted  for  pollination  by  this  insect. 

5.     Precise  adaptation  between  flowers  and  insects,  leading  to 

mutual  dependence. 

It  will  have  been  noticed  ere  this  that  the  flowers  which 
are  very  irregular  or  have  closed  corollas,  or  secrete  their 
nectar  at  the  bottom  of  deep  and  narrow  tubes  or  spurs, 
have  fewer  visitors  than  those  that  are  open  and  regular. 
Only  those  insects  which  have  long  proboscides,  or  which 
are  endowed  w4th  special  ability  at  forcing  passageways 
can  obtain  their  stores.  Flowers  thus  specialized  receive 
the  usual  good  and  ills  of  specialization;  they  enjoy 
especially  efficient  aid  when  their  proper  visitors  are  abun- 
dant and  lack  it  when  these  are  scarce.  It  is  in  the  relations 
existing  between  these  most  highly  specialized  flowers  and 
their  few  guests  that  one  sees  the  most  remarkable  phe- 
nomena of  fitness  and  learns  the  extent  and  the  precision 
of  mutual  adaptation. 

Such  adaptations  are  peculiar  and  special,  and  no  general 
outline  can  be  given  for  their  study:  instead,  an  example 
will  be  detailed  and  a  few  suggestions  offered,  and  not  a 
formal  outline. 

For  example,  let  us  consider  the  pollination  of  the  marsh 
weed  commonly  known  as  turtleheads  {Chelone  glabra). 
Its  rather  large  white  flowers  are  arranged  in  four  vertical 
rows  at  the  top  of  the  leafy  stem.  They  are  strongly 
bilateral  and  have  abundant  pollen  and  nectar,  so  guarded 


3©  GENERAL   BIOLOGY 

by  a  nearly  closed  corolla  entrance  and  by  internal  barri- 
cades of  spines,  as  to  be  accessible  to  only  one  kind  of 
visitors — small  worker  bumblebees.  A  side  vieAv  of  a  single 
flower  is  shown  in  fig.  22a.  The  narrowly  three-lobed,  pro- 
jecting lower  lip  offers  an  alighting  place  for  the  bees  and 
the  reflexed  edges  of  the  corolla  mouth  offer  them  footholds. 
A  swollen  palate  upon  the  lower  lip  blockades  the  entrance 
ao^ainst  other  insects,  but  under  the  weight  of  the  worker 
bumblebee  this  is  depressed  sufficiently  to  allow  the  head 
to  be  thrust  into  the  median  groove  that  divides  the 
"palate,"  and  thereafter,  a  little  pulling  and  pushing  effects 
an  entrance.  The  queen  bumblebee  sometimes  tries  to 
enter,  but  can  only  get  her  head  inside:  she  is  too  big. 
Other  insects  that  are  small  enough  are  too  light  to  "tip  the 
beam,"  or,  entering,  are  barred  from  the  nectar  by  a  mat  of 
bristling  hairs  on  the  floor  of  the  corolla  and  by  dense 
fringes  of  spines  on  the  stamens:  so  that  the  worker 
bumblebees  have  a  monopoly. 

These  bees  serve  the  flower  well.  They  exhibit  a  maximum 
of  efficiency  in  effecting  cross  pollination.  The  stigma  of 
the  flower  projects  slightly  beneath  the  tip  of  the  upper  lip 
of  the  corolla.  The  pollen  is  carried  by  the  bee  in  a  great 
quantity  amid  the  hairs  on  the  top  of  its  prothorax.  It  will 
be  easily  understood  that  in  forcing  an  entrance  through  the 
narrow  passage,  this  pollen  mass  is  pushed  hard  against  the 
stigma.  A  single  visit  is  sufficient  for  complete  pollination 
of  a  flower. 

The  chief  means  whereby  the  flower  reserves  its  sweets 
for  proper  visitors  are  not  seen  from  the  outside :  and  these 
are  its  most  peculiar  and  special  devices,  such  as  are  taken 
least  into  account  in  the  preceding  studies  of  this  chapter. 
So  let  us  look  within.  Looking  at  the  flower  from  below  we 
can  see  within  the  narrow  corolla  mouth  the  anthers  stand- 
ing close  behind  the  tip  of  the  pistil  and  close  under  the  upper 


IXTERDEPENDENCE   OF   ORGANISMS 


31 


lip  ffig.  23a).     Figure  236  represents  the  stamens  and  pistil 

inside  view  with  the  corolla  cut 
away.  The  stamens  are  re- 
duced to  two  pairs  and  a  hairy 
rudiment  of  the  fifth.  The  ar- 
row in  the  figure  indicates  the 
position  of  the  bumblebee  when 
it  is  inside  feeding,  its  body  be- 
tween the  paired  stamens,  its 
long  proboscis  reaching  down- 
ward to  the  nectaries  in  the  bot- 
tom. Only  the  bee  in  action 
could  explain  the  purpose  of 
some  of  the  peculiarities  of  these 
stamens.  They  are  laterally 
flattened  so  that  they  will  easily 
bend  aside.  Their  planes  are 
set  aslant  at  an  angle  opening 
forward,  so  that  the  bee  may 
easily  crowd  between  them.  The 
conspicuous  bend  forward  in 
their  middle  portion,  being  convex  toward  the  entrance,  is 
set  in  opposition  to  the  pushing  of  the  bee  so  that  they  may 
not  be  crowded  backward  out  of  place.  Now  turning  the 
stamens  so  as  to  see  them  from  the  front,  as  in  fig.  23^;,  we 
observe  that  the  space  between  them  is  much  narrower 
than  the  bee's  body.  Separating  them  a  little  with  our 
forceps,  as  at  fig.  22)d  we  observe  that  the  anthers,  held 
together  by  matted  hairs  above,  rotate  upon  their  stalks, 
separate  below,  exposing  their  pollen  cavities,  out  of  which 
a  shower  of  dry  pollen  falls.  Thus  it  is  the  bee  gets  dusted 
on  the  back.  One  may  demonstrate  this  by  thrusting  a 
pencil  of  the  thickness  of  the  bees  body  into  the  flower  and 
getting  a  deposit  of  pollen  upon  the  end  of  it.     Smaller 


Fi 'r.  23.  Diagrams  illustrating 
the  structure  and  mechanism 
of  the  turtle  heads  flower,  a, 
anthers;  p,  pistil;  r,  a  rudi- 
mentary fifth  stamen.  Other 
things  explained  in  the  text. 


32 


.GENERAL   BIOLOGY 


insects  would  not  be  large  enough,    and   weaker  ones  would 

not  be  strong  enough  to  swing 
open  the  heavy  doors  of  the 
pollen  cupboard:  so  this  flower 
reserves  its  pollen  as  well    as   its 

y  i,^     '^ ^  nectar    for     its      special      guests 

/  ^     y^/  and   afifords   us   a    good  example 

of  mutual  fitness  and  exclu- 
siveness. 


Study  5.  A  case  of  precise 
adaptation. 

This  is  an  individual  study,  to 
be  undertaken  only  when  condi- 
tions are  right — proper  flowers 
abundant,  warm  and  sunshin}^ 
weather,  etc.  A  highly  special- 
ized flower  with  its  nectar  not 
easily  accessible  to  flower  visitors 
should  be  selected,  and  it  should 
abound  in  freshly  blooming 
clumps ;  for  the  visits  to  such  flow- 
ers are  often  few  and  far  between. 


Fig.  24.  Diagrams  illustrating 
the  structure  of  the  ordinary 
flower  of  the  violet  (Viola 
ciiciiUatd).  a,  a  front  view 
of  the  flower  with  the  tip  of 
the  saccate  petal  cut  away, 
showing  the  blockade  of 
hairs  around  and  above  the 
stigma;  b,  lateral  view  with 
petals  and  sepals  in  part  re- 
moved; c,  the  same  more  en- 
larged, and  with  the  lateral 
stamens  removed;  d,  one  of 
the  spurred  stamens;  drop- 
lets of  nectar  on  its  outer 
side  shown  at  0,  and  pollen 
cavities,  at  p. 


The  Record  of  this  study  may 
well  consist  of  a  few  drawings  to 
illustrate  the  structure  of  the 
flower  and  the  details  of  the  en- 
trance, of  the  feeding,  and  of  pollen 
transference  by  its  visitor,  with  copious  explanations  there- 
to. 

6.     Specialization  miscarried. 
Among  our  showy  flowers  are  a  few  possessing  the  charac- 
teristics which  elsewhere  we  find  associated  with  insect  aid 
in  pollen  distribution,  and  which  are  never  or  rarely  visited 


INTERDEPENDENCE   OF  ORGANISMS  ^^ 

by  insects.  Such  an  one  is  the  common  blue  violet  (Viola 
cucullatd).  Other  species  of  violets  are  commonly  visited 
by  bees;  and  this  one  is  apparently  finely  adapted  for  such 
visitation.  Yet  the  bees  rarely  visit  it,  and  the  showy 
flowers,  being  incapable  of  self-pollination,  produce  no 
seed. 

The  accompanying  figures  show  the  structure  of  the 
flower.  It  is  strongly  bilateral,  with  a  saccate  lower  petal  en- 
veloping two  spurred  stamens :  it  is  blue,  with  pretty  "guide 
marks"  about  the  entrance:    it  secretes  a  little  nectar,  and 

exhales  a  slight  perfume :  its  entrance  is 
blockaded  against  improper  visitors, 
but  it  is  narrowed  and  curved  conven- 
iently to  admit  the  proboscis  of  a  bee 
standing  head  downward  upon  its  front. 
Furthermore,  it  is  well  adapted  to 
profit  by  the  bee's  visits.  A  proboscis 
plying  between  the  spurs  of  the  two 
Fig  25.    Tip  of  pistil      lower  stamcns  would   dislodo^e  the   dry 

of  the  violet  as  seen  °  ^        •' 

from  the  front,      pollen  from  thc  authcrs,  and  catch  it  as 

showing      pollen         . 

pushed  into  the  hoi-      it  falls,  and  Carry  it  out,  and  when  prob- 

low  of  the  stigma. 

mg  the  sac  of  the  next  flower  visited, 
would  deposit  it  on  the  stigma:  for  the  stigmatic  surface 
is  contained  in  the  hollow  of  the  pistil  tip,  turned  toward 
the  entrance  (fig.  25);  the  lower  edge  of  it  would  scrape 
up  pollen  from  an  entering  proboscis,  but  would  only  evade 
pollen  that  was  being  withdrawn.  What  better  device 
could  be  imagined  for  securing  cross  pollination  ? 

The  trouble  with  the  mechanism  is  that  it  no  longer 
works.  The  bee  stays  away.  Did  it  visit  the  flowers,  it 
would  transfer  their  pollen  perfectly  and  they  would  be 
very  fertile.  This  anyone  may  demonstrate  by  transfer- 
ring the  pollen  with  a  tooth  pick  and  watching  the  result  in 
seeds  produced.     The  failure  seem.s  to  lie  farther  back  in 


34 


GEXERAL   BIOLOGY 


the  physiology  of  the  plant ;    it  secretes  but  a  little  nectar 
— that  little  on  the  outside  of  the  spurs — not  enough  to  run 
down  into  the  sac  where  the  bee's  proboscis  can  reach  it. 
There   is,  however,   a    small    bee-fly    {Bomhylius  major) 

that  is  able  to 
get  the  nectar 
which  hangs  in 
minute  droplets 
on  the  outside  of 
the  spurs  (fig. 
26).  It  is  often 
seen  poising  be- 
fore a  flower, 
making  an  ob- 
lique thrust  at 
each  side  of  the 
entrance,  push- 
ing its  excessive- 
ly slender  proboscis,  not  down  the  proper  middle  passage- 
way at  all,  but  between  the  spur  and  the  wall  of  the  sac. 
Thuq,  it  touches  neither  stigma  nor  pollen,  and  gets  the 
nectar  without    doing  the  flower  any  service  in  return. 

But  even  if  this,  our  commonest  violet,  has  been  deserted 
by  its  proper  visitors,  and  left  to  the  comradeship  of  nectar 
thieves,  if  its  fine  adaptations  have  become  useless  and  its 
pretty  flowers  are  left  to  waste  their  diminished  'sweetness 
on  the  desert  air,'  the  plant  has  not  been  without  resource: 
after  the  showy  flowers  of  spring  cease  to  appear,  it  devel- 
ops at  the  surface  of  the  soil  minute  self-fertilizing 
(clistogamous)  flowers,  which  shun  the  light,  never  rise  up 
into  view  and  never  open,  but  which  are  abundantly 
fertile,  and  are  produced  all  summer  long^  (fig.  27). 


Fig.  26.     A  beefly  {Bombylius  major)  visiting  the  violet 
tlower. 


*These  clistogamous  flowers  will  be  examined  in  Study  51. 


INTERDEPENDENCE  OF  ORGANISMS 


35 


These  brief  studies  of  the  relations  between  flowers  and 
insects  should  have  made  it  apparent  that  we  have  with  us 
all  grades  of  association  from  the  most  casual  contact  to 
mutual  dependence,  and  that  we  have  all  grades  of  fitness 
on  both  sides :  further  that  while  the  adaptations  are  often 
wonderfully  intricate  and  fit,  they  rarely  work  perfectly, 
and  may  even  wholly  miscarry.  And  while  gratified  in 
observing  that  they  often  work  with  delightful  precision, 


Fig.  27.  Flowers  and  fruit  of  the  violet.  The  ordinary  blue 
flower  and  a  seed  capsule  (from  a  hand  pollinated  flower) 
shown  above;  a  row  of  clistogamus  flowers  shown  below; 
the  lowest  one  in  full  bloom. 

we  should  not  overlook  the  fact  that  the  simpler  plans 
suffice  for  the  maintenance  of  the  species  that  are  less 
specialized. 

II.       GALLS. 

Galls  are  abnormal  growths  of  plant  tissues  occasioned 
by  stimuli  external  to  the  plant  itself.  The  stimuli  are 
furnished  by  a  great  variety  of  insects,  by  a  few  parasitic 


36  GEXERAL  BIOLOGY 

fungi,  and  by  a  number  of  other  less  important  and  less 
common  agencies.  All  parts  of  the  plant  are  subject  to 
these  malformations. 

As  the  raking  of  a  wire  against  a  tree  trunk  that  is  swayed 
back  and  forth  by  the  wind  causes  great  ridges  to  grow 
upon  the  sides  of  the  trunk,  so  the  gnawing  or  sucking  of  an 
insect  in  the  growing  tissue  of  the  plant  causes  a  gall  to 
grow.  Not  all  irritations  to  plant  tissues  cause  such  over- 
growths, but  only  such  as  are  applied  while  the  tissue  is 
rapidly  developing.  There  are,  for  example,  a  number  of 
moth  larvae  that  work  in  the  stems  of  goldenrods:  those 
whose  attack  is  made  before  the  stem  tissues  are  fully  formed 
cause  galls;  the  others  are  merely  stem  borers.  Like- 
wise, in  oak  leaves  the  little  fly  larvae  that  attack  them 
in  the  bud  cause  galls;  the  later  ones  make  only  leaf 
mines.  The  stimulus  might  be  the  same,  but  the  period 
of  response  on  the  part  of  the  plant  being  overpast,  there  is 
no  gall  formation.  Overgrowth  of  the  plant  tissue  is, 
therefore,  the  criterion  of  a  gall. 

So  generous  is  the  response  of  the  plant  in  the  pro- 
duction of  tissue  that  serves  for  both  food  and  shelter, 
that  the  habit  of  attacking  young  tissues  has  been  biologi- 
cally profitable.  Hence  there  is  developed  a  large  fauna 
especially  and  exclusively  adapted  for  exciting  galls  and 
living  in  them — a  very  favorable  subject  for  the  study  of 
interrelations. 

Vie  will  confine  our  study  here  to  those  malformations 
that  are  caused  by  insects  and  mites,  notwithstanding 
that  there  are  some  common  and  conspicuous  galls,  like 
the  one  on  the  sumach  top  shown  in  figure  28,  made  by 
fungi.  This  one  belongs  to  that  general  class  of  galls 
popularly  known  as  "witches'  brooms":  other  common 
fungus  galls  appear  as  knots  and  swellings  upon  the  trunk 
or  the  branches  of  trees :  all  consist  of  more  or  less  solid  tissue 


INTERDEPENDENCE   OF  ORGANISMS 


37 


and  are  readily  distinguishable  from  animal  galls  which 
contain  distinct  cavities  for  the  occupancy  of  the  gall 
makers.* 


Fig.  28.     A  fungus  gall  of  the  "witches  broom"  type  on  the 
smooth  sumac  (Rhus  glabra   ) 


*While  we  commonly  speak  of  the  gall  insect  or  fungus  as  a  "gall 
maker,"  we  are  not  unmindful  that  it  merely  furnishes  the  stimulus 
to  overgrowth  on  the  part  of  the  plant  itself. 


38 


GENERAL   BIOLOGY 


Animal  galls. — Animal  galls  are  less  diffuse.  Under  the 
stimulus  of  the  attack  of  the  insect  in  feeding,  the  tissue 
grows  rapidly,  producing  more  food:  moreover,  around 
the  point  of  attack  it  grows  and  shuts  in  and  covers  and 
protects  the  gall  maker.  Furthermore,  it  continues  to 
grow  and  shape  itself  into  symmetry,  its  final  form  often 
resembling  a  fruit.  More  remarkable  still,  it  often  de- 
velops unpalatable  substances  (such  as  tannin)  in  its  walls 
and  sharp  spines  upon  its  surface,  and  thus  protects  its 
enemy  the  gall  maker,  from  being  eaten. 

Most  animal  galls  are  small,  but  a  few  of  them,  such  as  the 

aphid  gall  of  the  cottonwood 
shown  in  figure  29,  grow  large 
enough  to  become  when  numer- 
ous, a  feature  of  the  winter  land- 
scape. This  one  is  formed  not 
about  a  single  aphid,  but  about 
an  aphid  colony;  and  its  irregu- 
larity is  doubtless  due  in  part  to 
the  grouping  of  individuals  in  the 
attacking  aphid  flock. 

The  commoner  forms  of  ani- 
mal galls  are  these: 

ffelted 


open 


mantle 


scroll 

pocket 

fluted 


gall 
gall 
sail 


covering  gall 


Fig.  29.      Winter  aspect  of  aphid 
galls  on  a  cottonwood  tree. 


closed 


simple 
nucleated. 


The  differences  between  these  forms  are  indicated  in  the 
following  diagram,  (fig.  30). 


IXTERDEPENDENCE  OF  ORGANISMS 


39 


The  primary  distinction  between  open  and  closed  galls 
lies  in  their  mode  of  origin.  In  the  open  gall  the  attack  is 
made  from  the  outside,  while  in  the  closed  gall  the  insect 
enters  the   tissue   bodily   and  feeds  inside:    ordinarily,  it 


Fig.  30.  Diagram  of  typical  form  of  galls.  a,  felted;  b,  scroll;  c,  fluted; 
d,  pocket;  e,  covering;/,  simple  closed;  g,  nucleated,  a  to  ^  are  open 
galls;  /and  g,  closed. 

enters  in  the  egg  stage,  the  egg  being  inserted  through  a 
puncture  in  the  epidermis.  In  the  open  gall  the  insect 
may  be  covered  and  inclosed  by  the  overgrowing  tissue, 
but  when  inside  the  gall  it  is  still  outside  the  leaf 
substance,  and  in  feeding,  stands  upon  and  punctures 
the  epidermis  with  its  piercing  mouthparts. 

Felted  galls  (fig.  3 1)  represent  a  low  degree  of  gall  develop- 
ment. They  occur  mostly  upon  leaves,  and  are  as. a  rule 
made  by  mites.  They  usually 
consist  of  a  slight  sacculation 
of  the  part  of  the  leaf  blade  that 
is  subject  to  attack,  and  the 
malformation  is  mainly  confined 
to  the  epidermal  cells,  which 
develop  a  wonderful  growth  of 
robust  plant  hairs  that  are 
twisted  and  matted  together  like 
felt,  whence  the  name.  The 
mites  clamber  around  and  feed 
between  the  bases  of  these 
plant  hairs. 

Mantle    galls     represent     a     better     development      of 
leaf   cover  for  the    gall   maker:     the     cavity    is     deeper 


Fig.  31.  A  felted  gall  (a, 
cross-section)  from  the  leaf 
of  button-bush  {Cephalan- 
thus  occidentalis)  and  the 
mite  (6)  which  causes  it. 


40 


GEXERAL   BIOLOGY 


and  more  completely  inclosed,  and,  usually,  not 
felted  within:  the  walls  often  rise  and  shape  them- 
selves with  marked  symmetry  and  even  beauty.  The 
four  names  given  in  the  table  as  types  of  mantle  galls  are 
but  convenient  designations  of  the  more  typical  forms  which 


Fig.  32.  Stem,  leaf  and  flower  galls,  a,  a  nucleated 
gall  on  the  twigs  of  white  oak  {Quercus  alba),  b,  a 
mantle  gall  on  the  leaves  of  witch-hazel  (Hama- 
melis  virginiana) ;  c,  simple  closed  galls  on  the 
flowers  of  goldenrod  (Solidago    nemoralis). 


often  inter-grade  or  combine  together  in  a  single  gall.  The 
scroll  gall  is  formed  by  the  uprolling  of  the  leaf  margin : 
the  fluted  gall,  by  the  furrowing  of  the  blade  (chiefly  along 
veins)  in  elongate  grooves.  The  pocket  gall  and  the  cover- 
ing gall  although  much  alike  in  appearance  are  most  unlike 
in  fact,  being  diametrically    opposite   in  their  manner  of 


INTERDEPENDENCE  OF  ORGANISMS 


41 


growth.  Atypical  pocket  gall  is  shown  on  the  witch  hazel 
leaf  in  fig.  3  2 .  It  is  formed  by  the  descent  of  the  tissue 
attacked  to  form  a  pocket  upon  the  leaf  blade: 
the  attacking  insect  is  carried  into  the  pocket,  which 
usually  dilates,  and  forms  a  spacious  chamber.  The 
covering  gall,  on  the  contrary,  rises  up  around 
the  point  of  attack,  and  covers  the  insect  over,  leaving  only 
a  small  aperture  at  the  top.  The  removal  of  a  pocket  gall 
leaves  a  hole  through  the  leaf:  the  removal  of  a  covering 
gall  leaves  only  a  superficial  scar. 

Closed  galls,  as  already  stated,  re- 
sult from  internal  attack :  the  cavities 
they  contain  lie  wholly  within  the 
plant  substance.  They  likewise  differ 
among  themselves  in  the  degree  of 
their  development.  The  simpler  ones 
(fig.  32c)  have  thin  walls,  of  the  ord- 
inary tissues  of  the  part  bearing 
them.  The  nucleated  galls  (fig.  32a) 
show  often  a  high  degree  of  differen- 
tiation of  parts.  There  are  often 
three  well  defined  layers  in  their 
walls:  an  inner  (when  mature)  very 
hard  layer  forming  the  "nucleus" 
whose  cavity  contains  the  gall  maker, 
an  intermediate  softer  and  more  or  less  spongy  layer, 
and  an  outer  hard  layer,  often  protected  with  spines 
and  hairs  and  ornamented  with  beautiful  colors.  The 
stone-like  nucleus  in  the  middle  and  the  form  and  color  of 
the  exterior  greatly  enhance  the  superficial  resemblance  of 
the  gall  to  a  fruit.* 


Fig.  33.  Compound  gall 
on  the  root  of  wild  let- 
tuce {Lactuca  spf) 


*It  is  to  be  noted  in  passing,  that  the  gall  when  fruit-Hke  almost 
invariably  resembles  the  fruit  of  some  kind  of  plant  other  than  the 
one  that  bears  it. 


42 


GEXERAL   BIOLOGY 


As  to  their  distribution  upon  the  plant,  galls  are  solitary, 
^as  in  fig.  32  a)  clustered  (as  in  fig.  32c),  or  compound  (as  in 
fig-  33)'-  "they  are  called  compound  when  they  contain 
separate  cavities  surrounded  by  confluent  walls. 

The  animals  that  produce  galls. — With  a  few  unimportant 
exceptions  the  animals  that  cause  galls  to  grow  belong  to  a 
single  family  of  mites  and  to  five  orders  of  insects,  Hemip- 
tera,  Coleoptera,  Lepidoptera,  Diptera  and  Hymenoptera. 
The  mites  are  very  minute    four-    or    eight- 
legged  creatures  without  distinction  of   head 
and  thorax  (fig.  3ih).     They  live  amid    the 
growth  of  matted  hairs  that  fills  the  cavity  of 
felted  galls. 

Hemipterous  gall  makers  are  aphids, 
psyllids,  etc.,  and  they  generally  live  within 
mantle  galls. 

Coleopterous  and  Lepidopterous  gall  mak- 
ers are  beetle  and  moth  larvae  respectively. 
They  are  but  a  few  stray  members  of  large 
families  that  are  not  much  addicted  as  a 
whole  to  the  gall  making  habit:  but  these 
few  make  comparatively  large  closed  galls, 
some  of  which  are  sure  to  be  encountered  in 
the  following  field  study. 

Dipterous  gall  makers  mainly  are  gall 
gnats (Cecidomyiidae),  with  a  few  scattering 
representatives  of  other  families.  Cecidomyiid  galls  are 
very  common,  and  of  the  utmost  diversity  of  structure 
and  appearance.  The  larvae  within  them  are  often  very 
small,  but  they  are  distinguishable  by  the  possession  on 
the  under  side  of  the  first  segment  behind  the  head  of  the 
so  called  "breast  bone,"  a  flat,  brown  horny  piece  that  pro- 
jects forT\'ard  toward  the  mouth  and  is  often  notched  at 
its  tip   (fig.  34). 


Fig.  34  Dia- 
gram of  a  gall 
midge  larva 
(family  Ceci- 
doniyiidcE  of 
Diptera),  in, 
the    so-called 

"breast  bone;" 
n, respiratory 
apertures. 


INTERDEPENDENCE  OF  ORGANISMS  43 

Hymenopterous  gall  makers  belong,  with  a  few  exceptions 
to  two  families,  Tenthredinidae,  saw  flies,  and  Cynipidae, 
gall  wasps.  Sawfly  larvae  make  rather  simple  closed  galls, 
w^hich  they  abandon  when  grown,  to  find  some  other  place 
of  transformation.  Gall  wasps  are  gall  makers  par  excel- 
lence. They  cause  the  most  perfect  nucleated  galls:  as  a 
family  they  are  most  completely  adapted  to  the  gall  making 
habit.* 

The  tenants  found  in  the  course  of  the  following  study 
occupying  the  galls  collected,  may  be  identified  by  the  stu- 
dent himself.  For  the  adults,  of  which  few,  if  any,  will  be 
found,  use  the  keys  of  any  good  manual  of  entomology. 
Pupae  if  found  may  easily  be  reared.  Place  them  uninjured 
in  a  glass  jar,  add  a  wet  sponge,  or  bunch  of  cotton  to  pre- 
vent drying  up,  and  tie  netting  (preferably  fine  swiss)  over 
the  top  of  the  jar,  and  let  them  stand  till  they  emerge  as 
adult  insects.  Larvae,  which  will  generally  be  found,  may 
be  identified  as  follows: 

Key  to  the  commoner  insect  larvae  and  mites  found  in  galls. 

A.  Body  short  and  thick:   legs  rather  long. 

B.   Head  fused  with  body  and  not  distinct;    legs  2  or  4 

pairs Acarina,  Mites. 

BB.  With  distinct  head:    legs  3  pairs  (Hemiptera). 

C.  Wing  pads  present,  projecting  at  right  angles  with 

the  body:  no   cornicles  on  abdomen.  .Psyllidae. 

CC.  Wing  pads  absent,  or  if  present,  laid  lengthwise  of 

the  body:  cornicles  often  present  (see  fig.  39)  .  Aphidae 

AA.   Body  cylindric,  worm-like:   legs  minute  or  none. 

B.  With  3  pairs  of  minute  legs  under  the  thoracic  seg- 
ments. 


*It  is  to  be  observed  that  there  is  not  a  single  family  of  insects 
whose  members  are  all  gall  makers:     Cynipidae  comes  nearest. 


44  GENERAL  BIOLOGY 

C.  With  a  brown  shield  covering  the  prothorax  above: 

body  armed  with  stiff  bristles 

Lepidoptera,nioth  larvae. 

CC.  Without  a  brown  prothoracic  shield. 

D.  With    rudimentary    legs    (pro-legs)    underneath 

some  of  the  abdominal  segments 

Tenthredinidae,  sawfly  larvae. 

DD.  With  no  abdominal  prolegs 

Coleoptera,    beetle  larvae. 

BB.  Legless. 

C.  With  a  distinct  head  segment :   body  arcuate,  white. 
D.   Body  segments  deeply  wrinkled:    head  brown: 

skin    dull    white, 

Coleoptera,     Family    Curculionidae,  weevils. 
DD.   Body  segments  smooth,  shining,  head  mostly 

white Cynipidae,  gall  wasp  larvae. 

CC.  With   the   head    segment   greatly   reduced,    very 

minute  or  wanting:    body  straight.  .  .  .Diptera. 

D.  With  the  ventral  piece    shown    in  fig.  34  Color 

often  red  or  yellow. .  .Cecidomyidae,  gall  gnats. 

DD.  Without   this   structure.     Color    white 

Other  dipterous  larvae. 

Despite  the  food,  cover,  and  defense,  provided  by 
the  plant  for  the  gall  maker,  the  fact  must  not  be  lost 
sight  of  that  the  creature  is  the  plant's  enemy.  The 
young  bur-oak  shown  in  figure  3  5  gives  evidence  of  this. 
Cynipid  galls,  growing  too  thickly  have  killed  the  ter- 
minal shoot,  and  the  lateral  shoots  are  taking  up  the 
growth.  Such  positive  injury  from  galls  is  rarely  seen,  how- 
ever, for  the"  gall  makers  are  kept  in  check  by  hosts  of  very 
efficient  parasites.  The  student  foUow^ing  the  field  work 
outlined  below  will  be  sure  to  come  upon  some  of  these 
parasites,  and  it  may  be  with  some  difficulty  that  he  will 
distinguish  which  is  parasite  and  which  is  gall  maker  in 


INTERDEPENDENCE   OF  ORGANISMS 


45 


some    cases.     The    parasites   are    all    Hymenoptera,    with 
larval  form  very  like  that  of  Cynipid  larvae    (see   key). 

Such        larvae 


galls 


found  in 
that  are  made 
by  insects  of 
other  orders 
m.ay  of  course  be 
set  down  at  once 
as  parasites.  In 
cynipid  ga  1 1  s  , 
which  will  give 
the  trouble, 
these  sugges- 
tions may  help: 
The  Cynipid  lar- 
va gen  e  r  a  1 1  y 
quite  fil  1  s  the 
central  cavity  of 
its  gall ;  the  par- 
asitic larva  is 
usually  consider- 
ably smaller :  the  cynipid  larva  is  very  strongly  arcuate  with- 
in the  cavity ;  the  parasitic  larva  is  generally  not  so  strongly 
bent. 

The  gall  when  grown  offers  often  a  place  of  shelter  and 
sometimes  a  place  of  development  to  other  insects  besides 
the  one  that  caused  it  to  grow.  Thus  new  interrelations  are 
brought  about.  Some  of  these  are  well  shown  by  the 
cone  gall  of  the  willow  (fig.  36),  whose  fleshy  scales  when 
green  furnish  forage  for  the  burrowing  larvae  of  several 
species  of  moths  and  sawflies,  and  when  dry  furnish  shelter 
and  a  place  of  incubation  for  meadow-grasshopper  eggs. 
Guest   gall-flies,    also,  develop    between    the  outer  scales, 


Fig.  35.  Clustered  galls  on  a  young  bur-oak.  Ob- 
serve that  the  central  shoot  is  not  putting  forth 
leaves  {Qiiercus  macrocarpa.) 


46 


GENERAL  BIOLOGY 


often  in  great  numbers:  and  each  of    these    species    has    its 

inevitable  train  of  parasites. 

All  these  forms  together  constitute  a 
miniature  animal  society,  dependent  on 
the  overgrowth  of  willow  tissue  that  re- 
sults from  the  attack  of  the  gall  midge. 

Study  6.     A  study  of  common  galls. 

Apparatus  needed:  A  scalpel,  or 
knife,  a  lens,  and  a  basket,  bag,  or 
very  capacious  pockets. 

Collect     afield     a  large   number    of 
galls,    bringing      into     the  laboratory 
enough  to   fairly  represent   each   kind 
found.     Search    such    trees    as    oaks, 
hickories,  lindens,  hackberries  and  wil- 
lows;   such    shrubs  as    sumach,  roses, 
Avitchhazels    and    dogwoods  and     such 
herbs     as     goldenrods,     ox-eyes,     and 
touch-me-nots. 
The  record  of  observations. — Select  a  dozen  or  more  species 
that    represent  best   the  general   phenomena  outlined   in 
the  preceding  pages,  and  write  down  their  characters  in  a 
table  prepared  Avith  the  following  column  headings : 

Name  of  plant. 
Part  of  plant  affected. 
Position  of  gall  on  this  part  (upper  or  lower 

surface  of  leaf,  etc) . 
Gall  type. 

Aggregation,  solitary,  clustered,  or  compound. 
Cavity  of  gall  (shape,  close  fitting,  etc.). 
External  coat,  armature,  etc. 
Special  structural  features,  if  any. 
Defences  against  foraging  animals. 


Fig.  36. — Diagram  illus- 
trating the  distribu- 
tion of  the  inhabitants 
of  the  cone  gall  of  the 
willow:  a,  the  gall 
maker,  b,  moth  larva. 
c,  sawfly  larva.  d, 
meadow  -  grasshopper 
eggs.  e,  guest  gall- 
midge  larvae. 


The  Gall 


The  Insect 


INTERDEPENDENCE   OF   ORGANISMS  47 

Order  to  which  it  belongs. 

Family. 

Solitary  or  gregarious. 

Stage  found. 

Parasites  or  hyper-parasites. 

Inquilines. 

Summarize  the  results  of  the  preceding  study  in  a  table 
of  the  orders  of  the  gall  makers,  prepared  with  the  following 
column  headings. 

Order  (of  insects,  or  mites) 

Mouth  parts  (biting  or  sucking) 

Habits  (solitary  or  gregarious). 

Gall  type. 

Then  state  any  relation  appearing  i)  between  type  of 
mouthparts  and  type  of  gall,  and  2)  between  order  of  insect 
and  type  of  gall. 

III.       THE    RELATIONS    BETWEEN    ANTS    AND    APHIDS. 

Aphids  are  familiar  plant  pests  which  infest  our  fields  and 
gardens.  They  are  minute  Hemiptera,  possessed  of  a  slen- 
der proboscis,  with  w^hich  they  puncture  soft  plant  tissues 
and  suck  out  the  sap.  Some  aphids,  which  attack  develop- 
ing plant  tissues,  Avill  already  have  been  found  in  the 
cavities  of  the  galls  to  which  they  give  rise.  All  are  gre- 
garious in  habits,  mainly  because  their  great  reproductive 
capacity  is  coupled  with  poor  power  of  locomotion.  Genera- 
tion after  generation  they  are  wingless:  but  when  the  time 
for  their  wide  dispersal  is  at  hand,  a  winged  generation 
appears,  w^hich  flies  freely  in  search  of  new  locations. 
Autumn  is  the  time  of  dispersal  of  most  species,  because  of 
the  general  failure  of  food  supply  at  that  time,  and  the 
necessity  of  relocation  for  winter:  but  the  failure  or  un- 
favorable alteration  of  food  supply  may  occasion  the  pro- 
duction of  a  winged  generation  at  any  time. 


48  GENERAL  BIOLOGY 

Individually  aphids  are  insignificant,  but  collectively 
their  drain  upon  the  plant  may  be  very  serious.  Each 
aphis  is  an  animated  sap  pump.  It  sits  quietly  on  bark  or 
leaf,  with  its  proboscis  immersed  in  the  green  tissues,  and 
pumps  by  the  hour,  scarcely  changing  its  place  or  moving 
by  more  than  an  occasional  sweep  of  its  long  antennae. 
Its  food  consisting  of  sap,  contains  considerable  sugar — 
much  more  indeed  than  the  creature  is  able  to  assimilate. 
This  excess  of  sugar  is  discharged  from  time  to  time,  along 
with  the  other  rejectamenta  and  excreta  of  the  body,  in 
fluid  drops  of  "honey  dew." 

Honey  dew  is  very  sweet  and  palatable.  It  is  gathered 
from  the  leaves  where  it  falls  by  ants,  bees,  wasps  and  other 
animals.  Bees  store  it  as  honey,  and  although  it  is  not  the 
best  of  honey  still  it  is  not  unwholesome,  and  men  eat  it 
gladly.  When  aphids  are  abundant  on  growing  trees 
honey  dew  is  often  secreted  in  large  quantities.  A  stidden 
jarring  of  an  aphid  covered  bough  may  cause  such  a  sudden 
and  simultaneous  discharge  by  the  aphids  that  the  honey 
dew  Avill  fall  in  a  shower  of  fine  spray.  It  often  covers  the 
lower  boughs  of  trees  and  the  bushes  beneath  them,  with  a 
shiny,  sticky,  sweet  coating. 

That  ants  have  a  "sweet  tooth"  everyone  knows  from 
observations  in  his  own  pantry  or  lunch  basket.  They  like 
honey  dew,  and  from  gathering  it  at  large,  they  have  passed 
to  gathering  it  at  its  source — from  the  aphids  themselves. 
The  relations  between  the  two  that  find  their  simplest  ex- 
pression in  chance  visits  by  ants  to  aphid  colonies,  become 
much  more  intimate  when  ants  begin  to  guard  and  care  for. 
the  aphid  flocks,  to  build  shelters  for  them,  or  to  share  their 
own  homes  and  fortunes  with  them. 

These  relations  may  be  grouped  in  three  categories : 

I.  The  chance  feeding  by  ants  on  the  honey  dew  offered 
by  aphids. — This  is  hardly  more   than  accidental    associa- 


INTERDEPENDENCE   OF  ORGANISMS 


49 


Fro.  37. — Aphid  colony  on  a  leaf  of  Ceanothus, 
attended  by  ants  seeking  honey  dew.  h,  a 
larva  of  a  syrphus  fly,  feeding  on  a  wingless 
aphid.  1',  a  winged  aphid.  /,  an  ant  patting 
an  aphid  with  its  antennae,  k,  the  empty 
skin  of  an  aphid  that  has  been  parasitized. 


tion.     It    may    be  recognized     in     an    aphid   colony  that 
is  attended  by  one  kind  of  an  ant  on  one  day,  by  another 

kind  on  another 
day,  and  is  part  of 
the  time  unattend- 
ed. 

2.  The  habitual 
guarding  of  aphid 
colonies  by  ants, 
safeguarding  their 
own  supply  of 
honey  dew. — This 
is  the  commonest 
type  of  association, 
and  the  one  easiest 
to  observe.  I  n 
summer  or  autumn,  on  many  a  curled  dock  orthistle  or  dog- 
wood bush,  wherever  ants  are  seen  gathered  together  upon 
the  green  foliage,  there  one  may  expect  to  find  on 
closer  inspection,  an  abundance  of  aphids  as  well. 
And  if  one  approach  quietly  and  watch  carefully 
he  may  see  the  ants  moving  about  among  the 
aphid  herd,  fondling  them  with  their  antennae,  patting 
or  stroking  an  individual  here  and  there,  and  obtaining 
sometimes  as  a  response,  the  extrusion  of  a  drop  of  honey 
dew,  which  is  lapped  up  as  soon  as  it  appears.  The  ants 
will  often  be  seen  to  drive  away  intruders — chiefly  winged 
parasitic  insects,  which  seek  to  lay  their  eggs  upon  the 
bodies  of  the  aphids.  They  will  even  rush  at  an  intruding 
finger,  and  attack  it  fiercely,  though  ineffectively,  with  their 
jaws.  Yet,  though  they  show  great  dash  and  courage  in 
dealing  with  any  parasitic  syrphus  fly  or  ichneumon  that 
ventures  too  near  the  flock,  they  show  a  sad  lack  of  insight 
in  allowing  the  egg,  when  one  has  been  successfully  laid  by 


so 


GENERAL   BIOLOGY 


the  parasite,  to  remain  where  placed,  and  the  fly  larva, 
when  hatched,  to  feed  openly  (fig.  T^jh)  upon  the  aphids. 
That  their  guardianship  is  often  eluded  may  be  seen  on  close 
inspection  of  almost  any  aphid  flock. 

3.  The  domestication  of  the  aphids  by  ants. — This  covers 
at  least  two  distinct  sorts  of  activities  on  the  part  of  the  ants : 
i)  the  building  of  shelters  and  enclosures  about  the  aphid 


Fig.  38.     Aphis  shed  on  twig  of  dogwood ;  photo  of  a  specimen  in  the  Cornell 
University  collection. 

flocks,  and  2)  the  safeguarding  of  the  development  of  individ- 
ual aphids  and  the  establishment  of  aphid  colonies. 
These  are  two  well  recognized  functions  of  all  animal  hus- 
bandry. 

Ant  sheds  are  built  usually  near  or  on  the  ground  about 
compact  colonies  of  aphids  (or  other  honey  dew  secreting 


INTERDEPENDENCE  OF  ORGANISMS  51 

Hemiptera)  so  as  to  completely  enclose  the  flock.  With 
but  a  few  small  openings  left  through  the  walls  for  entrance 
and  exit,  the  guarding  of  the  flock  is  easier  and  the  security 
of  the  flock  is  greater.  The  aphids  no  longer  "run  the 
range,"  but  are  kept  in  folds.  Excesses  of  heat  and  cold 
are  less  felt,  and  the  great  injury  from  exposure  in  rainy 
weather  is  largely  avoided.  The  ants  probably  reap  the 
usual  rewards  of  good  husbandry  in  the  larger  and  more 
constant  secretion  of  honey  dew. 

The  sheds  are  of  two  sorts  as  regards  the  materials  of 
which  they  are  made :  i)  earthen  sheds,  made  of  sand  grains, 
etc.,  stuck  together  with  wet  clay,  and  2)  felted  sheds  made 
of  interwoven  bits  of  shredded  plant  tissues.  Both  sorts 
are  often  placed  about  the  stems  of  bushes  (fig.  38)  and 
supported  on  branches  or  leaf  stalks. 

Finally,  there  is  a  permanent  association,  with  the  ants 
exercising  care  and  control  over  the  aphids  in  all  stages  of 
their  development.  This  is  complete  domestication.  The 
best  known  case  of  it  is  that  of  the  little  brown  ant  of  the 
fields  and  the  corn-root  aphis.  This  subterranean  aphid 
lives  on  the  roots  of  Indian  corn,  where  these  roots  traverse 
the  branching  passageways  of  the  nests  of  the  ants.  It  is  a 
hapless  creature  (fig. 39),  quite  incapable  of  uncovering  corn 
roots  for  itself,  or  even  of  finding  them  if  uncovered:  so, 
the  ants  excavate  the  soil,  making  lateral  foraging  chambers 
communicating  with  their  nest,  and  carry  the  aphids  in 
and  place  them  on  the  roots.  There  the  aphids  feed 
and  secrete  honey  dew  through  the  season,  and  in  the  fall, 
there  they  lay  their  eggs.  The  following  account  is  quoted 
from  a  report  on  corn  insects  by  Professor  Forbes,  to 
whom  our  knowledge  of  this  relation  is  chiefly  due : 

"These  eggs,  which  are  yellow  when  first  deposited, 
but  soon  become  shining  black,  and  turn  green  just  before 
hatching,   are  at  first  scattered    here    and    there,     as     it 


52 


GENERAL  BIOLOGY 


happens,  but  are  finally  gathered  together  by  the  ants  for 
the  winter  in  little  heaps,  and  stored  in  their  galleries,  or 
sometimes  in  little  chambers  made  by  widening  a  gallery  as 
if  for  storage  purposes.      If  a  nest  is  disturbed,  the  ants  will 

commonly  seize  the  aphid  eggs, 
often  several  at  a  grasp,  and  carry 
them  away.  In  winter  they  are 
often  taken  to  the  deepest  parts  of 
the  nest.  .  .  as  if  for  some  par- 
tial protection  against  frost:  but 
on  bright  days  in  spring  they  are 
brought  up,  sometimes,  within  half 
an  inch  or  less  of  the  surface,  some- 
times even  scattered  about  in  the 
sunshine,  and  carried  back  again  at 
night — a  practice  probably  to  be 
understood  as  a  means  of  hastening 
their  hatching.  I  "have  repeatedly 
seen  these  ants  in  confinement  with 
a  little  mass  of  aphid  eggs,  turn  the  eggs  about  one  by 
one  with  their  mandibles,  licking  each    carefully   as   if   to 


Fig.  39.  Corn  root  aphis 
{Aphis  maidiradicis) ,  wing- 
less female  x  14  (from 
Forbes.)  The  two  black 
processes  at  the  rear  are 
Cornicles. 


Fig.  40.     Corn  root  aphis,  winged  female  x  16  (from  Forbes) 


INTERDEPENDENCE  OF  ORGANISMS 


53 


clean  the  surface.  These  anxious  cares  are  of  course  ex- 
plained by  the  use  the  ants  makeofthe  root  louse  [aphid], 
whose  excreted  fluids  they  lap  up  greedily  as  soon  as  the 
young  lice  begin  to  feed. 

"That  the  young  of  the  first  generation  are  helped  by  the 
ants  to  a  favorable  position  on  the  roots  of  the  plants  they 

infest  is  quite  beyond  ques- 
tion. .  .  We  have  repeat- 
edly performed  the  experiment 
of  starting  colonies  of  ants  on 
the  hills  of  corn  in  the  in- 
sectary,  and  exposing  root  lice 
from  the  field  to  their  attention 
and  in  every  such  instance,  if 
the  colony  was  well  established 
the  helpless  insects  have  been 
seized  by  the  ants,  often  almost 
instantly,  and  conveyed  under 
ground,  where  we  would  later 
find  them  feeding  on  the  roots 
of  the  com. 

"I  need  hardly  say  that  the 
relations  above  described  be- 
tween the  corn-root  aphis  and 
these    ants  continue    without 
cessation  throughout  the  year." 

Thus  sequestered  from  parasites,  and  guarded  by  the  ants 
and  cared  for  at  every  turn,  this  long  unknown  aphid  has 
flourished  inordinately,  and  has  become  throughout  the 
great  "corn  belt"  a  serious  pest.  It  is  another  illustration 
of  man's  influence  in  disturbing  the  natural  balance.  Corn 
fields  have  replaced  the  native  prairies  and  woodlands  over 
wide  areas,  and  have  offered  opportunities  for  almost  un- 
limited increase  in  numbers  of  com  insects  that  were  doubt- 
less but  sparingly  distributed  before. 


Fig.  41.  Small  brov.-n  ant  (Lasius 
niger  alienus)  that  domesticates 
the  corn  root  aphis ;  worker,  x  8 
(from  Forbes). 


54  GENERAL   BIOLOGY 

Study  y.     Observations  on  ants  a^td  aphids. 

It  is  not  possible  to  give  a  hard  and  fast  outline  for  the 
study  of  these  phenomena :  for,  thoughwidespread,  they  are 
not  equally  available  at  all  times  and  everywhere.  It 
should  be  possible  to  find  anywhere  in  summer  a  number  of 
colonies  of  aphids  with  ants  in  attendance,  on  such  plants  as 
curled  dock,  milkweed,  thistle,  dogwood,  etc.  Ants  are 
easily  seen  when  running  about  over  green  vegetation,  and 
almost  always  there  will  be  found  flocks  of  aphids  (or  of  other 
honey  dew  secreting  hemiptera  with  which  the  ants  have 
similar  relations)  as  the  occasion  for  their  assembling. 

Such  an  association  being  found,  the  apparatus  needed 
will  be  a  low  power  magnifier  (such  as  a  reading  glass  is  ex- 
cellent) and  a  note  book,  and  the  things  to  be  observed  are: 

i)   The  ordinary  behavior  of  the  ants  toward  the  flock. 

2)  The  gentleness  of  the  ants  toward  individual  aphids: 
the  stroking  and  patting  of  them  first  with  the  antennae  and 
coming  closer,  with  the  palpi. 

3)  The  lapping  up  of  the  honey  dew  when  an  aphid 
responds  by  ejecting  it. 

4)  The  ferocity  of  the  ants  toward  intruders :  this  may  be 
tested  with  one's  own  finger. 

5)  The  stupid  indifference  of  the  ants  toward  the  eggs 
and  larvae  of  the  parasites. 

6)  The  general  inactivity  and  helplessness  of  the  aphids. 

7)  The  prevalence  of  (parchment  skinned)  parasitized 
individuals. 

If  aphid  sheds  can  be  found,  their  materials  and  con- 
vStruction  should  be  noted,  their  doors,  their  braces,  and 
their  shape  as  adapted  for  giving  a  maximum  amount  of 
foraging  surface  with  a  minimum  of  construction.  Some 
advantages  to  both  ants  and  aphids  can  readily  be  seen  to 
accrue  from  them. 


INTERDEPENDENCE  OF  ORGANISMS  55 

Root  aphids  can  usually  be  found  in  any  corn  field  where 
burrows  'of  the  little  brown  ant  are  common.  There  bur- 
rows are  easily  seen  after  a  rain,  when  the  ants  open  them  up 
and  toss  out  upon  the  surface  annular  mounds  of  little 
pellets  of  earth.  The  aphids  will  be  found  by  exposing 
some  of  the  com  roots  where  they  traverse  lateral  passage- 
ways ramifying  outward  from  the  ants'  nest.  The  ants  will 
usually  promptly  demonstrate  their  care-taking  function  in 
the  premises,  by  seizing  any  aphids  that  may  be  shaken  off 
from  the  roots  and  carrying  them  into  their  nests.  An  ac- 
count of  a  cage  that  may  be  used  for  rearing  such  mixed 
colonies  in  the  laboratory  will  be  foupd  in   the    appendix. 

The  record  of  this  study  may  well  consist  of  brief  notes 
on  the  things  observed. 


CHAPTER  II. 


THE  SIMPLER  ORGANISMS. 

To  understand  the  complex  phenomena  of  life  we  must 
seek  their  simpler  expressions.  The  relations  between  the 
higher  and  more  familiar  forms  of  life  are  very  intricate. 
The  bodies  of  such  plants  and  animals  as  we  have  been  ob- 
serving are  highly  organized — composed  of  many  parts 
having  special  functions.  How  shall  we  learn  what  are  the 
primary  parts  and  functions  of  living  things?     It  will  help 

us    to    distinguish    essentials 
Fig.  42.      ciosterium  if    our    first    qucst    be    made 

lunula,  c,  cytoplasm ;  .  r      i         i 

n,  nucleus;  w,   cell  auioug    orgauisms    oi    lowly 

wall;    r,    chlorophyl-  rry,         ■  ■,  -,        , 

bearing  protoplasm;  structurc.     i he smiplcr plants 

^,    pyrenoid;i;,  .  .         ....  -,1  , 

vacuole.  and  animals  live  m  the  water. 

We  have  already  learned  that 
the  main  gatherers  of  food  material  for  the  living 
world  are  green  plants.  The  simplest  green 
plants  are  the  algae ;    so  with  these  we  will  begin. 

SOME   TYPICAL  ALGAE. 

When  we  learn  to  recognize  them  we  can 
hardly  look  into  the  water  anywhere  without  seeing  algae. 
They  float  in  green  masses  upon  the  surface ;  they  hang  in 
graceful  drapery  of  verdure  on  submerged  branches;  they 
drip  in  globules  of  gelatine  from  twigs  that  are  lifted  out  of 
the  water:  they  rise  from  the  bottom;  they  lie  amid  the 
silt ;  they  trail  across  the  rocks  that  are  swept  by  the  cata- 
ract; they  cling  to  wave-beaten  piers  and  boulders;  they 
are  free-swimming,  and  come  in  our  water  supply;  and  they 
grow  and  flourish  in  the  bottle  of  clear  water  that  is  long  left 


THE   SIMPLER   ORGANISMS  57 

standing  on  the  window  sill.  It  is  not  hard  to  find  them  in 
great  variety  of  size  and  form,  and  in  great  beauty  and 
delicacy  of  organization. 

Closterium  (fig.  42)  is  a  very  pretty  simple  alga  that  is 
commonly  found  in  the  bottom  sediment  of  fresh  water 
ponds.  Although  very  small,  its  bright  green  color  and 
crescentic  form  make  it  easily  recognizable.  If  we  gently 
lift  up  from  the  pond  bottom  some  sticks  that  have  long 
lain  undisturbed,  and  shake  into  a  white  plate  filled  with 
water  the  silt  that  covers  them,  spreading  it  out  in  a  thin 
layer,  we  may  usually  find  Closterium  scattered  about  over 
the  plate.  It  is  visible  to  the  unaided  eye,  and  is  easily 
recognized  with  a  pocket  lens.  It  is  easily  reared  indoors 
in  a  cool,  well-lighted  place  in  a  jar  of  pond  water  sup- 
plied with  some  mud  from  the  pond  bottom,  and  this  is  the 
best  way  to  get  a  large  supply.  Enough  for  class  study 
may  usually  be  obtained  by  mounting  the  scrapings  of  silt 
from  submerged  leaves,  that  have  lain  long  in  clear,  well- 
lighted  water. 

A  few  specimens  transferred  to  a  slide  and  examined  with 
a  microscope  present  at  once  to  the  eye  some  important 
characteristics  of  green  plants.  The  crescentic  plant  body 
is  seen  to  be  encased  in  a  transparent  capsule,  the  cell  wall, 
with  a  green  substance  filling  the  greater  part  of  both  ends 
of  the  crescent,  leaving  a  transparent,  clear  band  across  the 
middle.  In  this  clear  band  on  closer  inspection  there  is 
seen  a  slightly  granular  substance  of  such  transparency  it  is 
at  first  easily  overlooked,  and  in  the  centre  of  it  is  a  round 
body  of  slightly  denser  consistency.  Although  so  inconspicu- 
ous, it  is  well  to  fix  attention  at  once  upon  these  latter 
structures,  for  they  represent  the  essentials  of  living  struc- 
ture. The  granular  mass  is  protoplasm  and  the  round 
body  within  it  and  forming  part  of  it  is  the  nucleus.  The 
green  substance  filling  and  obscuring  the  protoplasm  at  the 


58  GENERAL   BIOLOGY 

sides  is  chlorophyl,  and  the  transparent  capsule  inclosing 
the  whole  is  the  cell  wall.  The  whole  plant  thus  enveloped 
is  a  single  cell. 

Well  down  in  the  angle  toward  each  end  of  the  crescent 
will  be  noticed  also  a  round  droplet  of  watery  fluid  called 
a  vacuole,  in  which,  under  high  magnification  may  be  seen 
suspended  some  minute  crystals  in  continuous  (Brownian) 
movement. 

If  from  a  freshly  growing  Closterium  culture  a  number  of 
individuals  be  mounted  and  examined,  they  will  be  found 
to  differ  considerably  in  size  and  in  appearance  at  the  trans- 
parent middle  crossband  where  the  nucleus  lies.  Some  of 
the  larger  ones  will  shoAv  a  broader  clear  area  there,  or  an 
indentation  of  the  cell  wall  at  each  side,  or  a  constriction 
extending  entirely  across  the  cell,  cutting  it  more  or  less 
deeply  into  two  parts,  as  indicated  in  figure  43.  Closely 
examined,  this  process  will  be  seen  to  be  initiated  by  the 
division  of  the  nucleus  into  two  parts,  one  of  which  passes 

to  each  side  of  the  cross  band  and  into  the 
edge    of    the    chlorophyl.       The    deepening 


//^'^T'^^Tx^       constriction  thus  divides  the  mass  of  proto- 

l/^^^^r)r-^\\      plasm,  and  forms  two  smaller  cells  out  of  one 

/x^II^J^^I^^^      large  one.     Each  of  the  smaller  ones,  before 

the  separation,  is  lacking    in  the  crescentic 

symmetry  of  the  grown  plant,  the   newly 

Fig.  43.     Divi-       fomicd  end  being  blunter,  lacking  chlorophyl 

terium ;  succes-     and  vacuolc,  and   having  the   cell  wall  thin 

and  not  symmetrical  with  the  other  end. 
Reflecting  on  the  few  readily  observable  details  of  this  ap- 
parently simple  process  whereby  new  plants  are  produced, 
it  is  obvious  at  once  that  certain  of  the  structures  seen  are 
more  essential  than  others.  It  is  the  protoplasm  that  pas- 
ses on  unchanged  from  mother  cell  to  daughter  cells — both 
the  general  protoplasm  of    the  cell-body  (cytoplasm)  and 


THE   SIMPLER   ORGAXISMS  59 

the  nucleus.  About  the  new  end  a  new  cell  wall  is  formed, 
and  in  the  protoplasm  of  that  end  new  chlorophyl  develops- 
It  is  for  the  sake  of  the  protoplasm  that  these  other  parts 
exist.  The  normal  structure  is  regained,  during  the  period 
of  growth  which  ensues.  Little  is  directly  observable  except 
the    increase  in  size  of  the  plant. 

The  two  processes  of  growth  and  reproduction  so  simply 
shown  in  Closterium,  are  characteristic  of  all  living  organ- 
isms, and  are  their  most  distinctive  phenomena. 

Many  algae  consist,  like  Closterium,  of  cells  existing 
singly,  while  many  others  consist  of  numbers  of  cells  ag- 
gregated together  to  form  a  more  complicated  plant  body. 
But  whether  the  plant  cell  exist  alone  and  apart,  or  whether 
it  live  in  contact  or  in  combination  with  other  cells,  its 
parts  are  usually  those  seen  in  the  cell  of  Closterium: 

1.  Protoplasm  J  cytoplasm    1  usually 
"the  physical  basis  of  life"    (and  nucleus  J  inclosed  by, 

2.  The  cell  wall,  an  investing  capsule  of  transparent  cel- 
lulose which  envelops,  besides  the  protoplasm,  certain 
diverse  substances  of  greater  or  less  importance  that  may 
collectively  be  designated  as: 

3.  Inclusions,  the  more  important  of  which  are 

a)  the  cell  sap;  a  watery  fluid  which  fills  all  the 
spaces  (vacuoles)  unoccupied  by  the  more  solid  parts 
and  is  the  medium  of  exchange  of  food  and  waste 
materials. 

b)  chlorophyl,  the  greenish  substance  above  noted,  in 
the  presence  of  which  occur  carbon  reduction,  and 
the  storage  of  energy  of  the  sun's  rays  (to  be  dis- 
cussed under  a  subsequent  heading),   and 

c)  secretions,  excretions,  reserve  stores  of  starch  and 
other  food  materials,  precipitations  of  mineral  crys- 
tals, (such  as  oxalate  of  lime),  from  the  saturated 
solutions  of  the  cell  sap,  etc. 


6o 


GEXERAL   BIOLOGY 


The  two  studies  -which  immediately  follow  are  intended 
to  give  i)  an  acquaintance  with  the  appearance  of  the  living 
part  of  plant  substance,  and  2)   some  knowledge  at  first 

hand  of  the  diversity  of  form  of  cells  and 
of  the  manner  of  their  combination  to- 
gether into  a  plant  body  among  the  algae. 

Study  8.     The  cell    of  Spirogyra  and     the 
protoplasm    of  Nitella. 

Materials  needed — a  supply  of  fresh 
Spirogyra    and  Nitella  in  clean  water. 

Apparatus  needed — the  usual  labora- 
tory equipment  of  simple  and  compound 
microscopes,  small  tools,  glassware  and 
reagents. 

The  student  should  first  examine  Spir- 
ogyra in  mass,  as  it  lies  in  the  water,  and 
then  lift  out  a  small  tuft  of  its  long 
filaments  for  examination  in  water  upon  a 
white  plate.  He  will  there  note  their 
length  and  their  unbranched  condition. 
Examining  them  with  a  simple  lens,  he 
will  be  able  to  distinguish  clearly  the 
spiral  bands  of  green  that  wind  about  each 
filament  on  the  inside  and  make  Spirogyra 
easy  of  recognition  among  other  algae  of  similar  manner  of 
growth   (fig.  44). 

If  he  then  mount  a  few  filaments  upon  a  slide,  placing  a 
cover-glass  upon  a  favorable  portion,  and  filling  up  the 
space  beneath  the  cover  glass  with  water,  he  may  with 
advantage    apply    the    compound  microscope  to  the    ex- 


FlG.  44.  Spirog^^ra. 
a,  a  bit  of  a  filament 
containing  nine 
cells;  6,  a  single  cell, 
more  highly  magni- 
fied;  c,  cytoplasm; 
n,  nucleus;  p,  pyre- 
noids,  in  the  chloro- 
phyl   band. 


amination  of    them.* 


Placing 


the    slide    thus    prepared 


*If  the  student  be  not  familiar  with  the  use  of  the  compound 
microscope,  let  him  at  this  point  pursue  the  supplemental  study 
outlined  in  the  opening  pages  of  the  appendix,  for  which  Spirog^^ra  is 
appropriate  material. 


THE   SIMPLER  ORGANISMS  6i 

upon  the  stage,  and  examining  the  delicate  filaments  with 
low  power  of  the  microscope,  he  will  at  once  observe  that 
they  are  not  all  alike:  different  species  of  Spirogyra  often 
grow  together,  but  the  filaments  of  a  single  species  differ: 
some  are  of  a  richer  green,  with  the  chloroph}^  bands 
adjusted  closer  together  about  the  inner  walls  of  the  fibre. 
Let  him  select  for  study  a  filament  with  the  green 
bands  as  far  apart  as  possible  (so  that  the  internal  parts 
may  not  be  hidden)  and  examine  it  as  to  the  arrangement 
of  its  parts. 

The  cell. — It  will  be  at  once  apparent  that  the  plant  body 
is  composed  of  elongate  cylmdric  cells  placed  together  end  to 
end :  the  filament  is  a  simple  linear  aggregate  of  cells.  Look- 
ing at  a  single  cell,  it  will  be  seen  to  have  a  rather  thick  cell 
wall  squarely  cut  at  the  ends..  The  chlorophyl  is  restricted 
to  the  spiral  band,  which  is  not  continuous  from  cell  to  cell, 
and  which  varies  considerably  in  appearance  and  in  number 
of  turns  in  the  cells  of  different  filaments.  Focusing  upon  the 
upper  surface  of  the  cell,  the  chlorophyl  band  will  be  seen 
most  clearly — a  beautiful  wavy  band  of  green,  marked  with 
a  narrow  median  ridge,  and  studded  here  and  there  along 
the  course  of  this  ridge  with  round  bodies  containing  the 
pyrenoids.  Focusing  downward,  the  band  appears  below,  in- 
clined in  the  opposite  direction,  and  less  clear  becaUvSe  of  the 
parts  now  intervening.  Focusing  upon  the  axis  of  the  cell, 
and  looking  between  the  green  bands  for  the  more  funda- 
mental parts,  there  will  be  seen  (and,  readily,  when  one  be- 
gins to  see)  at  the  center  of  each  cell  a  mass  of  protoplasm 
containing  the  nucleus.  As  compared  with  the  size  of  the 
cell,  the  amount  of  cytoplasm  is  small.  It  consists  in:  i) 
the  central  mass  containing  the  nucleus,  2)  slender  strands 
radiating  outward  therefrom  to  various  parts  of  the  cell, 
but  chiefly  to  the  pyrenoids,  and  3)  a  thin  film  next  the  cell 
wall.  This  last  fits  the  cell  wall  so  closely  and  is  so  trans- 
parent it  is  hard  to  see.     It  may  be  drawn  into  view  by 


62 


GENERAL   BIOLOGY 


osmotic  pressure,  if  one  only  replace  the  water  beneath  the 
cover  glass  with  some  denser  liquid,  such  as  dilute  glycerine, 
or  5%  salt  solution.  This  outer  film  will  then  be  seen  to 
shrink  away  from  the  cell  wall,  and  if  the  shrinkage  con- 
tinues, to  collapse  altogether;  but  if  replaced  quickly  in 
pure  water,  it  is  soon  restored  to  its  original  condition; 
clearly  the  larger  part  of  the  cell  is  occupied  with  the  watery 
cell  sap,  easily  withdrawn  or  replaced. 

Thus  the  main  features  of  structure  may  be  seen  in  the 
living  cell.  But  the  relations  of  some  of  the  more  delicate 
parts  may  be  made  more  clear  by  the  two  following  experi- 
ments. If  a  drop  of  iodine  solution  be  placed  upon  the 
fibres  upon  the  slide,  it  will  stain  the  protoplasm  yellowish 
brown,  making  the  peripheral  parts  of  it  more  apparent. 
It  will  also  stain  the  minute  starch  granules  that  lie  about 
the  edges  of  the  pyrenoids  dark  blue  or  blackish. 

If  a  few  fresh  green  filaments  be  placed  in 
strong  alcohol,  the  chlorophyl  will  be  dissolved 
out  by  the  alcohol  (more  rapidly  with  the  aid 
of  heat)  and  the  protoplasmic  matrix  in 
which  the  chlorophyl  is  held  w411  be  apparent. 
Nitella. — In  order  to  get  a  large  enough 
single  mass  of  pure  protoplasm  to  see  without 
lenses  and  to  handle,  it  is  necessary  to  find 
cells  much  larger  than  the  ordinary  ones,  that 
shall  contain  it.       The    common    stonewort. 


Nitella,  is  an  alga  with  some  very  large 
(multinucleate)  cells,  from  which  the  proto- 
plasmic content  is  easily  removable,  and  may 
well  be  used  for  a  first  direct  observation  on 
protoplasm.  Nitella  grows  upon  submerged 
limestone  rocks  in  permanent  water.  It  is  one 
of  the  most  highly  organized  of  the  algae.  It  is 
attached  at  its  base,  bears  branches  arranged 


w 


Fig.  45. 

ella. 
tip 


Nit- 
a,  the 
of     a 


branch;  b,  a 
bit  of  the 
same  some- 
what mag- 
nitied;  n  , 
node;  i,  t, 
intemodes- 


THE  SIMPLER  ORGANISMS  63 

in  whorls  along  its  stem,  grows  apically  from  terminal  buds, 
and  has  more  of  the  aspectof  familiar  plants  of  other  groups 
than  any  of  the  algae  studied  hitherto.  An  examination  of  its 
structure  (fig.  45)  will  reveal  that  its  stems  and  its  branches 
are  alike  made  up  of  alternating  nodes  and  internodes,  the 
nodes  consisting  of  a  ring  of  short,  closely  packed  cells,  the 
internodes  consisting  each  of  a  single  very  large  and  long 
cell.  The  branches  arise  from  the  nodes.  The  internodes 
are  wholly  exposed. 

It  is  these  very  large  internodal  cells,  with  their  consider- 
able quantity  of  contained  protoplasm  that  we  will  study. 
Since  they  are  wholly  exposed  to  view  and  have  more  or 
less  transparent  walls,  it  will  be  well  to  observe  first  the 
movements  of  the  living  protoplasm  as  seen  under  low 
power  of  the  microscope.  A  fresh  green  spray  may  be 
plucked  from  the  top  of  the  stem,  placed  upon  one  slide  and 
held  flat  under  another  laid  upon  it,  and  thus  placed  upon 
the  stage  for  observation.  Focusing  upon  the  upper  sur- 
face of  an  internodal  cell,  just  beneath  the  roughness  of  the 
cell  wall  will  be  seen  the  numerous  oval  green  chlorophyl 
bodies.  At  a  slightly  lower  level,  by  looking  intently  for  a 
minute,  there  may  be  seen  the  streaming  protoplasm,  which, 
though  itself  transparent,  contains  munute  granules,  by  the 
movement  of  which  it  may  be  recognized.  These  granules 
will  be  observed  to  have  a  slow,  flowing  or  gliding  motion, 
and  they  may  be  traced  in  a  definite  path  of  circulation 
round  about  the  wall  of  the  cell.  A  comparison  of  different 
internodal  cells  will  show  that  the  streaming  movement 
varies  in  rapidity  in  different  ones  and  is  much  more  clearly 
seen  in  some  cells  than  in  others.* 


*In  case  Nitella  be  not  obtainable,  the  closely  allied  Chara  (Fig. 
48)  may  be  used  for  the  foregoing  study:  but  for  observation  of 
the  streaming  protoplasm,  single  internodal  cells  will  usually  be 
found  only  at  the  tips  of  the  leaves. 


64  GENERAL   BIOLOGY 

The  protoplasm  may  be  rem.oved  from  an  internodal  cell 
by  snipping  off  one  end  of  it  with  scissors  (after  it  has  been 
wiped  dry)  and  squeezing  the  contents  out  upon  a  slide. 
The  largest  available  cells  should  be  selected,  for  even  then 
the  drop  of  protoplasm  obtained  is  a  minute  one.  Still  it  is 
large  enough  to  see  and  to  handle.  One  may  lift  it  on  the 
point  of  a  needle,  and  test  its  viscosity.  One  may  see  it 
with  the  microscope,  wholly  uncovered.  And  if ,  in  looking 
at  it,  there  is  little  to  be  seen,  there  is  enough  to  reflect  upon 
in  the  fact  that  this  inert  and  apparently  well-nigh  structure- 
less mass  is  the  essential  living  part  of  every  living  thing, 
much  the  same  in  all,  and,  despite  appearances,  the  builder 
of  all  the  array  of  organic  life.  It  is  this  substance  that  in 
the  long  aeons  of  the  past  has  reclaimed  the  earth,  and 
clothed  it  with  verdure  and  peopled  it. 

The  record  of  the  foregoing  study  may  well  consist  in 
drawings  of  some  of  the  things  seen,  such  as: 

A  few  filaments  of  Spirogyra,  showing  their  common 
features  and  the  individual  differences  between  them. 

A  single  Spirogyra  cell  showing  all  the  parts  in  detail. 

A  bit  of  the  chlorophyl  band,  highly  magnified,  show- 
ing its  form,  the  median  ridge  upon  it,  the  py- 
renoids,  and  starch  granules. 

A  cell  treated  with  dilute  glycerine,showing  the  shrunken 
protoplasmic   capsule  withdraw^n  from  the  cell  wall. 

A  diagram  of  the  internodal  cell  of  Nitella,  showing 
the  direction  of  the  protoplasmic  current. 

THE  FORM  OF  THE  PLANT  BODY  IN  COMMON   ALGAE. 

Some  hints  of  the  diversity  of  form  in  algae  will  have 
been  gained  from  the  study  of  Closterium,  Spirogyra  and 
Nitella — the  first,  unicellular;  the  second,  a  linear  aggre- 
gate, its  cells  all  alike;  and  the  thijd,  a  branching,  well-in- 
tegrated body  of  cells  of  very  different  sizes,  with  terminal 
buds    and  apical  growth. 


THE   SIMPLER  ORGANISMS 


65 


8 


The  form  of  the  plant  body  is  much   influenced  by    the 

manner  of  cell  division.  When 
the  cells  separate  completely  at 
division,  the  plant  remains  per- 
manently unicellular.  AV  h  e  n 
elongate  cells  divide  transverse- 
ly, and  remain  attached,  the 
linear  aggregate  results:  when 
they  divide  lengthwise,  such 
rafts  as  those  of  Scenodesmus 
(fig.  46)  and  of  many  diatoms 
H'  ^  TkT  result.     When  the  planes  of  di- 

^  /^  vision  of  the  cells  of  a  linear  ag- 

gregate become  oblique,  cutting 
off  from  the  cells  prolonged  api- 
cal angles,  the  filaments  become 
branched  as  in  Cladophora  (fig. 
47).  When  no  division  planes 
are  formed,  only  the  nucleus, 
but  not  the  cytoplasm  dividing, 
overgrown  multinucleate  cells 
are  formed.  One  such  t3^pe, 
that    is  enormously   overgrown 


Fig.  46.  Miscellaneous  algae, 
further  illustrating  types  of 
cell  form  and  arrangement,  a, 
Clathrocystis,  actively  divid- 
ing; b,  Scenodesmus  acutus;  c, 
Scenodesmus  caudatus;  d,  Sele- 
nastrum;  e,  Hydrodictyon,  /, 
Cosmarium;  g,  Staurastrum; 
h,  Euastrum. 


in  long  irregular  interlacing  fibres,  is 
Vaucheria,  the  green  felt — an  alga 
that  is  found  abundantly  on  wet  soil 
in  greenhouses. 

One  observes  in  studying  the  algae 
that  the  transition  from  unicellular 
to  multicellular  forms  is  very  gradual. 
First,  there  are  multitudes  of  single, 
completely  independent  cells.  Then 
there     are    those   algae     that     consist 


Fig.  47.  Cladophora 
s  ,  a  branch; 
t,  a  tip  from  the 
same,  to  show  cell 
arrangement. 


66 


GEXERAL    BIOLOGY 


of  practically  independent  cells  that  merely  hang  together. 
Then  there  are  those   that   show  some    differentiation  of 

parts,  and  some  mutual 
relations  between  them. 
See  node smus  caudaius 
(fig.  46c)  shows  a  very 
moderate  beginning  of 
differentiation  in  the 
modified  form  of  the 
two  end  cells.  Then 
we  have  a  dift'erentia- 
tion  betw^een  base  and 
apex,  the  one  end  tak- 
ing up  the  duty  of  se- 
curing attachment,  the 
other  providing  for 
growth  as  in  Cladophora 
(fig.  47).  Finally,  w^e 
have  in  Chara,  a  solid 
aggregate  of  greatly 
differentiated  cells.  Chara,  like  Nitella,  is  made  up 
of  a  succession  of  nodes  and  internodes,  but  in  the  former 
there  is  one  central  cell  completely  surrounded  laterally 
by  a  layer  of  slenderer  cells  (fig.  48).  Thus  the  central 
cell  is  completely  inclosed  and  removed  from  the  source  of 
supply  of  food  and  air;  and  it  is  rendered  dependent  on  its 
neighbors  for  its  living.  And  in  Chara  and  in  many  other 
algae  there  is  a  high  degree  of  division  of  labor, 
certain  cells  of  the  plant  body  being  set  apart  to  serve  the 
reproductive  process,  w^hile  others  perform  the  nutritive 
functions. 

The  purpose  of  the  following  study  is  to  observe  in  a 
variety  of  representative  algae  the  phenomena  of  cell  aggre- 
gation and  of  cell  differentiation.     Incidentally  there  should 


Fig.  48.  Chara.  a.  a  small  branch,  b.  a 
piece  of  the  stem  containing  a  node  and 
part  of  two  internodes,  the  lower  one  hav- 
ing the  cortical  cells  spread  apart  from 
the  central  cell;  o,  ovary  (archegonium) ; 
s,  spermary  (antheridium) :  c,  the  mature 
ovary  more  enlarged,  showing  the  egg  cell 
within;  tf,  e,  and /,  successive  stages  in  the 
,  development  of  the  ovary:  g,  the  mature 
spermary  in  section;  h.  a  pair  of  sper- 
matic filaments;  i,  a  bit  of  one  of  the 
filaments  more  magnified  to  show  the 
sperms  developing  within  the  cells;  ^,  a 
single  sperm,  set  free. 


THE  SIMPLER  ORGANISMS 


67 


be  seen  something  of  the  place  algae  occupy  in  the  world, 
something  of  their  diversity  of  form  and  size,  something 
of  their  exquisite  beauty  and  delicacy  of  organiza- 
tion, and  the  principal  differences  between  them  in  the 
manner  of  their  chlorophyl  distribution. 

Study  g.     Observations  on   cell  form  and   growth 

habit  in  algae. 

The  materials  needed  are:  i.  A  few  of  the  larger,  more 
typical  green  algae  (such  asNostoc,Cladophora,  Hydrodic- 
tyon,  Vaucheria  and  Chara)  in  water. 


Fig.  49.  Some  water-supply  diatoms,  i".  Navicula; 
/  Cocconema;  k,  Asterionella;  /,  Tabellaria;  m, 
Fragilaria.  ^ 

2.  Some  submerged  or  floating  leaves  of  aquatic  plants, 
from  which  may  be  scraped  a  variety  of  diatoms  and  des- 
mids.  The  student  will  get  these  for  study  by  mounting 
and  examining  the  scrapings  upon  a  slide.  Stalked  diatoms 
may  usually  be  found  upon  the  filaments  of  the  larger  algae, 
such  as  Cladophora. 

3.  Strainings  from  the  water  tap,  yielding  diatom.s  (fig. 
49)  and  other  algae  that  are  common  in  the  water-supply, 
obtained  by  tying  a  sac  of  fine  silk  bolting  cloth  over  the  tap 
and  letting  the  water  run  slowly  through  for  an  hour  or  less. 

The  study  should  consist  in  the  examination  by  the  stu- 
dent of  these  different  algae,  one  by  one,  observing  and 
recording  the  points  outlined  above.  He  will  find  it 
desirable  to  familiarize  himself  somewhat  with  the  princi- 


68 


GENERAL   BIOLOGY 


D 


E 


pal  groups  of  algae  by  reference  to  any  good  text  book  of 
botany.  The  identifications  of  unusual  forms  that  may  be 
found  will  be  facilitated  by  the  use  of  the  plates  in  such 
works  as  AVolle's  Fresh  Water  Algae,  Wood's  Fresh  Water 

Algae  of  North  America 
West's  British  Fresh  Water 
Algae,  and  keys  in  such 
works  as  Lam.pert's  Das 
Leben  der  Binnengewasser 
and  Stokes'  Analytical  Key 
to  the  Genera  and  Species 
of  the  Fresh  Water  Algae 
and  Desmidiae  of  the  Uni- 
ted States. 

The  record  of  the  results 
of  this  study  may  be  pre- 
served in  a  few  simple  out- 
line drawings,  showing  for 
the  larger  forms,  a  diagram 
of  the  manner  of  growth, 
and  a  drawing  showing 
the  cell  form  and  the  distribution  of  chlorophyl.  Nucleus, 
protoplasm,  cytoplasm,  and  other  internal  parts  may  be 
taken  for  granted,  and  need  not  be  sought  out  nor  repre- 
sented in  this  record. 

SOME  TYPICAL  PROTOZOANS. 

The  simplest  animals  are  the  Protozoans.  In  a  much 
greater  proportion  than  in  the  algae,  the  cells  exist  singly. 
Like  the  unicellular  algae  they  consist  of  few  parts,  and  such 
of  those  parts  as  they  have  in  common  are  found  in  every 
cell — nucleus,  cytoplasm,  inclusions,  etc. 

Amoeba  (fig.  51)  is  one  of  the  simplest  of  animals.  We 
call  it  an  animal  because  it  moves  about  freely  and  feeds  on 
other  organisms ;   but  at  first  sight  it  seems  wholly  lacking 


Fig.  50.     Micrasterias  (after  Carpenter.) 
A  to  F,  successive  stages  in  cell  formation. 


THE  SIMPLER  ORGANISMS  69 

in  the  usual  features  of  animal  life.  It  has  no  legs,  nor  even 
muscles,  for  moving,  no  mouth  for  eating,  no  nerves  for  feel- 
ing, no  organs  whatever  for  any  purpose.  Since  the  amoeba 
lives  an  essentially  animal  life  without  these  parts,  a  careful 
study  of  it  may  enable  us  to  discover  what  are  the  essentials 
of  animal  existence. 

Probably  the  easiest  of  the  amoebas  to  obtain  for  study  is 
the  small  species  that  develops  in  a  hay  infusion.  If  a 
quantity  of  dry  hay  be  put  into  a  jar  of  water  and  left  stand- 
ing uncovered  where  not  exposed  to  the  direct  rays  of  the 
sun,  soon  the  soluble  organic  matter  in  the  hay  is  dissolved 
by  the  water.  In  the  course  of  a  day  or  two  the  bacteria 
that  feed  on  this  solution,  form  a  soft  jelly-like  substance 
which  gathers  in  a  film  upon  the  surface  of  the  water  in  the 
jar.  In  the  course  of  about  three  days  amoebas  begin  to 
appear  commonly  in  the  jelly  layer,  moving  about  therein 
and  feeding  on  the  bacteria.  In  another  day  or  two  they 
generally  reach  their  maximum  of  abundance ;  but  they  may 
continue  much  longer,  if  the  conditions  of  their  living  be 
maintained. 

They  are  too  small  to  be  seen  with  the  unaided  eye,  and 
hence,  must  be  mounted  upon  a  slide  and  looked  for  with 
low  power  of  the  compound  microscope.  Since  they  inhabit 
the  under  part  of  the  surface  layer  of  bacterial  jelly,  they  are 
best  obtained  free  from  it  on  the  slide,  by  lifting  a  little 
patch  of  the  jelly  upon  the  slightly  separated  tips  of  a  for- 
ceps, dabbing  it  down  several  times  on  a  slide,  thus  shaking 
off  the  drop  of  adherent  water  and  the  amoebas  with  it,  and 
then  throwing  the  mass  of  jelly  away.  Even  thus,  so  much 
of  the  jelly  may  have  fallen  into  the  drop ,  that  one  will  have 
to  look  about  the  thin  edges  of  it  to  find  a  clear  field  for 
observation  of  the  animals. 

It  is  very  important  that  the  temperature  of  the  animals 
be  not  lowered  during  the  process  of  mounting  them  or  of 


70 


GENERAL   BIOLOGY 


observing  them  later;  else,  the  following  observ^ations  will 
not  be  possible :  for  if  they  be  cooled,  they  will  contract  into 
a  heap,  and  remain  inactive  and  scarcely  recognizable. 
Therefore,  the  air  of  the  room  in  which  they  are  studied,  and 
the  slide  and  cover  and  stage  of  the  microscope  must  not 
be  cooler  than  the  water  from  which  they  are  taken. 

In  a  few  moments  after  their  transfer  to  the  slide  (the 
drop  being  properly  covered,  and  the  space  beneath  the 
coverglass  entirely  filled  with  water)  the  amoebas  should  be- 
gin to  creep  around  freely  upon  the  sur- 
face of  the  glass.  Although  very  minute 
they  will  be  recognized  even  under  low 
power  by  their  form  (see  fig.  51)  and 
especially  by  their  slowly  changing  out- 
lines. The  details  of  internal  struc- 
ture in  a  single  animal  are  not  to  be  ob- 
served except  with  high  magnification, 
and  a  sufficient  cutting  down  of  the  light 
to  allow  the  more  transparent  parts  of 
the  animal  to  come  into  view.  When 
found  and  properly  lighted,  it  will  be  easy 
to  recognize  in  the  body  a  granular  cen- 
tral mass  of  protoplasm,  a  clearer  exterior  layer,  with 
definite,  though  slowly  changing  outline  that  never  shows 
sharp  angles,  but  only  rounded  lobes. 

The  granular  internal  portion  of  the  body  of  the  animal 
is  spoken  of  as  the  endosarc.  Within  it  are  to  be  seen 
i)  the  round  and  uniformly  translucent  nucleus:  2)  the 
very  clear  contractile  vacuole,  which  disappears  at  intervals, 
and  which  usually  shows  a  tinge  of  pinkish  color,  and 
3)  ingested  food  particles,  usually  aggregated  more  or  less 
into  round  food  balls  which  may  be  seen  moving  about  in 
the  endosarc.  In  these  food  balls  the  forms  of  some  of 
the  bacteria  more  recently  eaten  may  usually  be  recognized^ 


Fig.  51.  Amoeba,  a, 
an  active  individ- 
ual; ps,  pseudopo- 
dium;  m,  nucleus;/, 
food;  V,  vacuole; 
b,  diagrammatic 
representation  of 
division. 


THE   SIMPLER  ORGANISMS 


71 


Different  individuals  will  differ  much  in  clearness  of  these 
parts,  according  as  they  have  recently  eaten  much  or  little. 
The  very  clear  external  protoplasmic  layer  is  generally 
known  as  ectosarc.  It  shows  no  definite  cell  wall,  but 
only  an  enveloping  film ;  hardly  more  of  this  than  may  be 
accounted  for  by  surface  tension  of  the  body  fluids.  It 
has  in  amoeba  developed  no  external  skeleton,  but  remains 
so  clear  that  we  may  here  observe  nearly  simple  naked 
protoplasm,  unobscured  by  anything,  and  in  action.  The 
movements  seen  here  are  quite  different  from  the  simple 
streaming  motion  in  a  single  current  of  the  intemodal  cell 
of  Nitella;  they  are  of  a  higher  order  of  complexity.  A 
portion  of  the  body  substance  may  be  pushed  out  in  any 
direction,  but  always  in  the  direction  of  locomotion,  forming 


Fig.  52.  Amoeba.  Diagram  illustrating  in  /,  2,  3,  food  intake; 
in  4,  3,  6,  removal  of  indigestible  residue;  s,  a  food  organism; 
p,  the  same  occupying  a  food  vacuole,  recentlv  engulfed;  g,  the 
same  partly  digested;  r,  residue  of  same,  discharged. 

the  broadly  rounded  lobes  called  pseudopodia:  first  the 
ectosarc  pushes  out,  and  then  the  granular  endosarc  streams 
forward  into  it.  Pushing  out  forward,  and  pulling  up  from 
the  rear  is  the  process  of  locomotion,  and  it  is  dependent 
solely  upon  the  contractility  of  protoplasm. 

By  this  same  power  feeding  is  accomplished.  Two 
pseudopodia  (fig.  52  J-j)  encircle  a  suitable  bit  of  food,  and 
press  it  into  the  interior  of  the  body,  where,  engulfed  by  the 
protoplasm,  it  is  digested :  any  indigestible  residue  is  gotten 
rid  of  by  the  reverse  process — the  protoplasm  flows  away 
from  it  and  leaves  it  behind  (fig.  52  4-6). 

These  activities  imply  volition  of  some  sort  or  degree, 
for  there  appears  to  be  some  selection  of  food  and  some 
spontaneity  of  movement:    changes  of  direction,  the  taking 


72  GENERAL  BIOLOGY 

of  a  circuitous  course  in  avoidance  of  an  obstruction, 
etc., indicate  this,  and  since  there  is  only  protoplasm  present 
and  responsible  for  the  actions,  it  follows  that  sensibility, 
or  at  least,  the  capacity  for  responding  to  external  stimuli, 
is  another  property  of  protoplasm.  We  tap  the  slide 
sharply  and  the  amoebas  contract,  drawing  in  their  pseudo- 
podia,  but  soon,  after  a  different  interval  in  different  indi- 
viduals, they  resume  activity  again. 

The  larger  amoebas  live  in  the  sediment  on  the  bottom  of 
ponds  and  ditches,  in  the  slime  on  the  submerged  leaves  of 
aquatic  plants,  etc.,  and  while  much  more  difficult  to  obtain 
in  sufficient  numbers  for  class  use,  they  are,  on  account  of 
their  size,  much  more  favorable  for  studies  of  some  of  the 
phenomena  outlined  above.  One  gets  specimens  for  study 
by  mounting  the  slime  upon  a  slide  and  searching  till 
amoebas  are  found.  Since  these  commonly  devour  diatoms 
and  desmids,  which  show  their  characteristic  colors  for  a 
time  after  being  engulfed,  the  process  of  digestion  (as  ev- 
idenced by  the  disappearance  of  the  normal  plant  structures) 
is  in  these  species  more  easily  observed. 

Study  10.  The  structure  mtd  activities  of  Paramoecitim. 
Materials  needed:  A  hay  infusion  a  week  or  more  old 
in  which  the  surface  layer  of  the  bacterial  jelly  is  breaking 
up,  being  largely  consumed,  and  in  which  Paramoecium  has 
appeared  in  large  numbers:  or,  an  old  infusion  that  has 
been  kept  going  by  occasional  feeding  with  corn  meal.  The 
paramoecia  will  be  found  about  the  edges  of  the  culture 
close  to  the  surface.  They  are  large  enough  to  be  seen  as 
minute  oblong  white  specks  in  rapid  motion.  They  must 
be  present  in  sufficient  numbers  for  one  to  get  a  number 
in  a  drop  of  water  taken  up  by  a  pipette,  and  if  not  so 
numerous,  they  should  be  concentrated,  by  some  such  sort 
of  filtering  apparatus  as  that  described  in  the  appendix. 
There  will   be    needed    also,    besides    the    usual    labora- 


THE   SIMPLER  ORGANISMS  73 

tory  apparatus  and  reagents,  a  little  dry  carmine,  and  a 
2%   solution  of  gelatine,  or  its  equivalent. 

The  student  should  perform  the  work  of  the  following 
outline : 

1.  Obtain  a  drop  of  water  containing  paramoecia  upon  a 
slide.  Examine  it  uncovered  with  a  simple  lens  to  make 
sure  that  the  animals  desired  are  present.  A  little  trash 
from  the  jar  included  in  the  drop  will  be  of  assistance  in  pre- 
venting the  cover  glass  from  coming  down  too  close  and  crush- 
ing the  animals.  Numerous  smaller,  but  similar  infusorians 
are  likely  to  be  associated  with  Paramoecium,  and  often  the 
phenomena  of  division  are  more  commonly  found  among 
these. 

2.  Before  applying  the  cover  glass,  survey  the  contents 
of  the  drop  with  low  power  of  the  compound  microscope, 
and,  by  moving  the  slide,  follow  some  of  the  paramoecia  as 
they  go  swimming  about.  Observe  the  spiral  course  of  the 
swimming,  and  the  resultant  rapid  motion  directly  forward. 
Observe  also  the  habit  of  the  animal  when  it  meets  an  ob- 
struction :  note  the  slight  backward  motion  before  the  turn- 
ing aside. 

3.  Apply  the  coverglass.  with  plenty  of  water  under  it, 
so  that  there  will  still  be  room  for  swimming.  Find  a  place 
where  a  paramoecium  is  repeatedly  meeting  with  obstruc- 
tion to  his  swimming,  and  observe  what  relation  the  direc- 
tion of  his  turning  aside  bears  to  the  position  of  the  oblique 
groove  {oral  groove)  down  one  side  of  the  anterior  end  of  the 
body.  Observe  also,  the  rolling  motion  of  the  body  in 
swimming,  and  determine  what  relation  the  position  of  the 
mouth  bears  to  the  axis  of  the  spiral  couise  in  which  the 
animal  swims. 

4.  Withdraw  some  of  the  water  from  under  the  cover- 
glass  with  a  blotting  paper  strip  held  at  the  edge,  so  as  to 
confine  some  of  the  animals  in  close  quarters.     Find  a  place 


74  GENERAL  BIOLOGY 

where  several  may  be  observed  together,  the  movements  of 
all  somewhat  restricted.  Note  the  perfect  definiteness  of 
anterior  and  posterior  ends  of  the  body.  Note  the  general 
pliancy  of  the  body,best  seen  when  turning  sharp  corners.etc. 

5.  Observe  the  presence  of  a  sharply  defined  layer  of 
ectosarc,  thickly  covered  over  its  outer  surface  with  minute 
transparent  hair-like  processes  called  cilia  in  constant  rapid 
motion.  To  the  lashings  of  these  cilia,  the  movements  of 
the  animal  are  due.  The  cilia  are  invisible  in  too  strong 
light,  and  also  when  in  rapid  motion;  in  the  latter  case  the 
scattering  of  such  minute  particles  as  come  near  them  will 
testify  to  their  presence  and  activity.  A  few  longer  cilia  at 
the  hinder  end  of  the  body,  seem  to  serve  as  a  sort  of  steer- 
ing apparatus  or  rudder,  and  probably  assist  in  keeping  to  a 
true  course  in  swimming. 

6.  Observe  the  position  and  relations  of  the  oral  oiroove, 
its  length,  its  oblique  position,  and  the  funnel-shaped  depres 
sion  in  which  its  posterior  end  terminates.  Observe  the 
peristome  surrounding  the  mouth,  bearing  a  continuous  line 
of  larger  and  stouter  cilia,  which,  besides  their  participation 
in  the  spiral  swimming,  drive  food  particles  into  the  funnel- 
shaped  mouth  opening. 

7.  Mount  a  small  drop  of  clean  water  containing  para- 
moecia  in  a  large  drop  of  gelatine  solution  upon  a  slide, 
cover  and  study  the  action  of  the  cilia.  The  movements  are 
restrained  more  or  less  by  the  gelatine,  and,  with  proper 
lighting,  should  be  easily  observed. 

8.  In  a  quiescent  but  living  specimen  observe  the  large 
vacuole  near  either  end  of  the  body.  Watch  it  long  enough 
to  observe  its  contraction  and  disappearance,  and  the 
formation  of  the  circle  of  radiating  clefts  through  the  sur- 
rounding protoplasm.  Consider  the  part  such  movements 
may  play  in  keeping  the  contents  of  the  cell  in  circulation. 

9.  Observe  also  the  nuclei  nearer  the  centre  of  the  body. 
The  nucleus  is  differentiated  into  tw^o  part? ;   a  large  oval  or 


THE   SIMPLER  ORGANISMS  75 

oblong  meganucleiis  and  a  little  round  micronucleus  close 
beside  it.  The  former  at  least  should  be  visible  in  the  live 
animal. 

10.  Mount  another  drop  of  clear  water  containing 
paramoecia,  first  adding  to  it  a  little  finely"  powdered  car- 
mine, stirring  the  carmine  through  the  drop.  Cover,  remove 
excess  of  water,  find  a  little  group  of  paramoecia  in  some 
more  or  less  restricted  area,  among  trash,  or  at  the  edge  of 
the  cover,  and  watch  them  eat  the  carmine.  It  is  wholly 
indigestible  and  may  be  followed  in  its  entire  course  through 
their  bodies.  Unless  the  mounting,  stirring,  covering  and 
finding  be  done  with  unusual  celerity,  bright  red  food-balls 
of  carmine  will  already  be  seen  within  the  protoplasm  of 
the  animals  when  first  looked  at.  Other  food-balls  may  be 
seen  forming  in  the  neck  of  the  funnel-shaped  rudimentary 
esophagus  that  leads  inward  from  the  mouth,  and  those  first 
formed  may  be  seen  in  their  course  of  circulation  round  the 
body,  and  may  in  a  little  while  be  followed  through  their 
entire  circuit. 

11.  Mount  another  drop  containing  paramoecia,  adding 
thereto  a  little  methyl  green  or  iodine.  Cover  and  study 
carefully  the  details  of  cellular  structure : 

a)  Ectosarc  and  endosarc. 

b)  The  peristome  and  its  fringing  cilia,  and  the 
esophagus. 

c)  The  cilia  of  the  body  in  general  and  of  the  posterior 
end  in  particular. 

d)  The  stinging  threads  which  the  reagent  used  caused 
to  be  thrown  out  from  the  ectosarc.  These  will  be 
seen  among  the  cilia  along  the  sides  of  the  body,  and 
will  be  distinguishable  therefrom  by  their  irregularity 
and  unevenness  of  length,  and  by  their  different 
mode  of  attachment  to  the  ectosarc. 

e)  Meganucleus  and  micronucleus. 

f)  Vacuoles  and  food-balls. 


76 


GENERAL  BIOLOGY 


12.  In  a  fresh  mount  containing  a  large  number  of  indivi- 
duals study  the  division  of  Paramoecium  (or,  if  more  abun- 
dantly evidenced,  use  any  other  available  infusorian). 
Observe  the  division  of  both  mega-  and  micro-nucleus,  and 
the  subsequent  division  of  the  protoplasm.  Observe  the 
fate  of  the  oral  groove.  The  different  stages  may  often  be 
found  simultaneously  in  different  dividing  individuals. 

The  record  of  this  study  may  well  consist  in : 

1.  A  diagram  to  illustrate  the  spiral  course  of  swimming 
of  Paramoecium. 

2.  A  diagram  to  illustrate  the  movements  by  which  an 
obstruction  is  avoided.  Indicate  plainly  oral  and  aboral 
sides. 

3.  A  detailed  drawing  of  a  single  animal,  showing  all  its 
normal  structures.  This  should  be  begun  with  the  begin- 
ning of  the  study,  and  details  added  as  they  are  worked  out. 

4.  A  series  of  outline  drawings  illustrating  the  progress  of 
division. 

Study  II.      The   specialized  cell-body  of  Stentor  and 

Vorticella. 

It  will  now  be  Avell  to 
study  a  few  of  the  higher 
protozoans,  illustrating 
the  great  degree  of  dif- 
ferentiation of  parts  and 
of  specialization  that 
may  occur  in  the  single 
free -living  cell.  For 
this  purpose  two  com- 
mon protozoan  inhabi- 
tants   of     fresh     water 

-."*'xG.  53.     Three    common    infusorians.     A,  A       fC,               \                    1 

Paramoecium;  n,  nucleus;  v,  v,  vacuoles;  pOnClS     (ng.     53/     ^irC    SCl- 

/,   food-ball  at  the  bottom  of  the  rudimen-  ^       -     j            Oi         -_                        1 

tary  esophagus;  /?,  peristome.     C.  Stentor;  leCted,          btCntor          and 

/,  lorica.     F,    Vorticella;   s,  extended;  t,  -r,-       ,  .       ^^ 

contracted.  VortlCalla. 


THE  SIMPLER  ORGANISMS  77 

Stentor. — This  is  a  large  protozoan  that  is  often  found 
adherent  to  submerged  twigs  and  leaves,  and  that  is  usually 
obtained  by  placing  the  trash  from  a  pond  in  jars  of  water 
and  letting  it  stand  a  few  hours.  The  stentors,  large 
enough  to  be  seen  w^th  the  unaided  eye,  and  to  be  cer- 
tainly recognized  with  a  pocket  lens,  w^ill  be  found  extended 
in  the  form  of  a  trumpet,  the  narrow  basal  end  attached  to 
the  twigs,  etc.,  or  suspended  beneath  the  surface  film.  If  a 
twig  bearing  stentors  attached  be  transferred  to  a  slide, 
covered,  and  allowed  abundance  of  room  and  plenty  of 
water  beneath  the  cover,  the  stentors  will  soon  be  ready  for 
observation,  and  for  the  work  of  the  following  outline: 

1.  Make  a  preliminary  survey  of  the  contents  of  the 
mount,  finding: 

a)  Stentors  extended  and  trumpet  shaped  (whence  their 
name),  and  attached  by  their  slender  bases  to  some 
support. 

b)  Others  contracted  into  globular  or  club-shaped 
form.  If  possessing  a  gelatinous  cup-shaped 
receptacle  about  theii'  bases  of  the  sort  known  as  a 
lorica  (fig.  53  C,  ^), these  will  be  more  or  less  with- 
drawn into  it. 

c)  Others  detached,  more  or  less  contracted,  and  lying 
free  or  swimming  about  in  the  water  with  something 
of  the  spiral  rolling  motion  of  Paramoecium.  These 
may  have  been  detached  in  mounting;  however, 
Stentor  may  voluntarily  make  a  change  of  base. 

2.  Find  a  little  group  that  may  be  brought  into  the  field 
with  the  lowest  power  of  the  microscope,  and  take  time  to 
study  their  actions: 

a)  While  watching  a  fully  extended  animal  through 
the  microscope,  tap  or  jar  the  slide  sharply  and  see 
it  contract :  continue  watching  until  it  is  again  fully 
extended. 


78  GENERAL  BIOLOGY 

b)  Observe  the  action  of  the  fringe  of  strong  cilia  (peri- 
stome)  surrounding  the  rim  of  the  trumpet,  and  try 
to  see  objects  free  in  the  water  driven  by  these  cilia 
into  the  mouth.  If  not  well  seen  this  may  be  demon- 
strated, as  for  Paramoecium,  by  adding  a  little 
finely  pulverized  carmine  to  the  water. 

3.  Using  an  eyepiece  of  higher  magnification,  study 
the  extended  stentor,  observing: 

a)   The  lorica,  if  present;    note  its  shape,  appearance, 

and  consistency. 
h)  The  disc-like  attachment  of  the /(9c^. 

c)  The  long  tapering  body,  covered  with  minute  cilia, 

d)  The  flaring  distal  end,  with  its  encircling  peristome, 
involute  at  one  end  to  surround  the  mouth.  Com- 
pare with  the  peristome  and  mouth  of  Paramoecium. 

4.  AVithin  the  body  observe  in  a  specimen  having  the 
mouth  uppermost: 

a)   The  short  esophagus  ending  blindly  in  the  endosarc. 
h)   Food -balls  moved  about  in  the  endosarc. 

c)  An  elongate,  moniliform  meganucleus,  and  a  micro- 
nucleus  close  beside  it.  The  latter  is  usually  hard  to 
see  in  the  living  specimen,  but  may  be  demonstrated 
with  iodine  as  in  Paramoecium. 

d)  A  large  contractile  vacuole,  of  varying  proportions. 

e)  Fine  nearly  parallel  lines  extending  from  foot  to 
disc  in  the  ectosarc  (myonemes) . 

5.  Observe  the  ordinary  reproduction  of  the  animal  by 
division  of  the  single  cell  into  two ;  note  the  plane  of  the  di^d- 
sion,  and  the  relation  it  bears  to  foot,  disc,  peristome  and 
meganucleus. 

The  Record  of  the  study  of  the  stentor  may  well  consist  in : 

1.  A  sketch  in  simple  outlines  of  a  little  group  of 
stentors  in  various  positions. 

2.  The  details  of  structure  of  a  single  animal. 


THE   SIMPLER  ORGANISMS  79 

3.  The  phenomena  of  division,  in  a  series  of  outhne 
sketches. 
Vorticella. — This  protozoan  will  usually  be  found  associa- 
ted with  Stentor  and  specimens  for  study  are  readily  ob- 
tained by  the  same  means.  The  individuals  are  smaller, 
and  singly  are  difficult  to  see ;  but  they  commonly  occur  in 
groups,  and  a  little  cluster  of  them  about  a  twig,  contracting 
so  strongly  as  to  almost  disappear  when  touched,  will  be 
easily  recognized .  Vorticellas  when  abundant  appear  to  the 
unaided  eye  as  a  whitish  fringe  about  the  edges  of  submerged 
twigs.  The  student  should  obtain  upon  a  slide  a  small  bit 
of  rootlet  or  other  solid  support  with  vorticellas  attached, 
should  mount  and  cover  this,  filling  "up  vrith  vvater  all  the 
space  beneath  the  cover,  and  then  should  perform  the  work 
of  the  following  outline : 

1 ,  Survey  the  mount  for : 

a)  Single  vorticellas  contracting  and  extending  their 
stalks. 

b)  Little  groups  of  individuals,  attached  to  the  rootlet 
separately. 

c)  Detached  heads,  broken  oft:  from  the  stalks  and 
swimming  free. 

2.  Study  the  actions  of  the  vorticellas,  observing: 

a)  The  contraction  and  subsequent  extension  of  the 
stalk. 

b)  The  closing  and  opening  of  the  peristome. 

c)  The  action  of  the  cilia  and  its  effects  on  free  particles 
in  the  water. 

d)  The  action  of  the  vorticellas  toward  one  another 
when  touched,  and  toward  other  free  swimming 
organisms  which  happen  to  come  into  contact  with 
them. 

3    Study  the  differentiation  of  pares  in  the  body  of  Vorti- 
cella, noting: 


8o  GENERAL   BIOLOGY 

a)  The  complete  differentiation  of  the  body  into  bell- 
shaped  "head"  and  contractile  stalk.  What  is  the 
distribution  of  ectosarc  and  endosarc  in  each  ? 

b)  The  great  development  of  the  peristome,  and  the 
restriction  of  the  cilia  thereto.  Note  the  size  of  the 
cilia,  and  the  contractility  of  the  ridges  that  bear 
them. 

c)  The  band  of  contractile  substance,  a  highly  de- 
veloped myoneme,  extending  in  an  open  spiral  down 
the  stalk.  Observe  its  position  in  extended  and  in 
contracted  specimens. 

4.  In  the  body  of  the  cell,  observe  the  usual  internal 
structures : 

a)  A  curved,  often  horse-shoe-shaped  meganucleus 
near  the  middle  of  the  body,  and  a  micronucleus 
lying  close  beside  it.  If  the  latter  be  not  visible  in 
the  living  specimen  it  may  be  demonstrated  later 
with  iodine,  as  in  Paramoecium. 

b)  A  clear  contractile  vacuole,  near  the  nucleus,  appear- 
ing and  disappearing. 

c)  Food-balls,  moved  about  within  the  endosarc. 
The  taking  of  food  and  the  formation  of  these 
balls  at  the  end  of  the  rudimentary  esophagus, 
may  be  demonstrated  by  feeding  with  carmine, 
as  in  Paramoecium. 

5.  By  surveying  a  large  cluster  of  vorticellas,  a  number 
are  likely  to  be  seen  in  process  of  division.  In  such  observe 
the  plane  of  division,  and  its  relation  to  nucleus,  peristome 
and  stalk. 

The  record  of  the  study  of  Vorticella  may  well  consist  in : 

1.  A  drawing  in  outline  of  a  little  group  in  various 
positions. 

2.  The  details  of  structure  of  a  single  cell  much 
enlarged. 


THE   SIMPLER  ORGANISMS 


8i 


3.  An  outline  drawing  illustrating  the  manner  of  dividing. 

Colonial  Vorticellidae. — In    a    number     of     protozoans 

allied    to     Vorticella,    the     two    cells    resulting    from    a 

division  do  not  entirely  separate, 
but  both  remain  attached  basally 
to  the  common  stalk,  each  later 
prolonging  the  atta  hment  into  a 
stalk  of  its  own.  Successive  divi- 
sions thus  give  rise  to  colonies.  Such 
colonies  are  likely  to  be  found  asso- 
ciated with  Vorticella,  and  should 
be  compared  therewith.  When  the 
colonies  are  large  they  are  easily 
distinguished  with  the  unaided  eye 
from  clusters  of  Vorticella  by  their 
height,  due  to  their  elevation  on  a 
common  stalk.  One  of  the  com- 
monest of  these  is  Epistylis,  dia- 
grammatically  shown  in  the  accom- 
panying figure  (fig.  54).  This 
differs  from  Vorticella  in  that  the 
stalk  is  not  contractile,  lacking 
the  myoneme:  myonemes  are  re- 
stricted to  the  base  of  the  elong- 
ated "head"  which,  becomes  trans- 
versely wrinkled  when  contracted, 
and  to  the  peristome  which  becomes 
enrolled,  as  in  Vorticella. 

In  Charchesium ,  however, 
the  individual  stalks  are  con- 
tractile and  in  Zoothamnium,  the  common  stalk  of  the 
colony  also,  in-so-much  that  when  Zoothamnium  contracts, 
the  main  stalk  and  all  its  branches  acting  synchron- 
ously, all  the  bodies  are  suddenly  brought  down  into  a 


Fig.  5.  EpistyHs  umbellarius. 
a,  a4portion  of  a  colony ;  x  and 
y,  successive  divisions  pro- 
ducing conjugants  of  reduced 
size;  s,  conjugation  between 
one  of  these  reduced  cells  and 
a  cell  of  normal  size,  b,  a 
single  individual  in  lateral 
view,  showing  the  elongated 
esophagus  and  peristome;  c, 
diagram  of  the  top  of  the 
peristome,  showing  its  spiral 
arrangement;  d,  a  normal 
individual,  contracted. 


82  GENERAL   BIOLOGY 

round,  berry-like  heap.     These  three  genera  include  all  our 
common  allies  of  Vorticella  of  colonial  habit. 

It  is  not  to  be  overlooked,  while  studying  protozoans, 
that  even  in  these  forms,  there  is  a  foreshadowing  of  the 
principal  organs  of  the  higher  animals.  The  long  esophagus 
of  Epistylis  is  prototype  of  the  alimentary  canal ;  the  con- 
tractile vacuole,  forerunner  of  a  sort  of  rudimentary  circula- 
tory apparatus;  and  the  myonemes  constitute  a  sort  of 
elemental  muscular  system. 

THE  LIFE  PROCESS  IN  PLANT  AND  ANIMAL  CELL. 

We  have  seen  that  in  many  algae  and  in  most  protozoans 
the  cell  is  an  independent  organism:  all  functions  of  plant 
or  animal  are  performed  by  it.  Even  when  such  cells 
are  grouped  together  to  form  a  larger  organism,  their  union 
is  for  the  most  part  a  loose  one,  and  their  physiological 
independence  is  little  impaired.  To  the  cell,  then,  we  must 
go  to  learn  what  are  plant  and  animal  functions,  and  how 
they  are  performed. 

How  does  the  cell  live  and  grow?  This  is  a  hard  question, 
answered  as  yet  only  in  part.  The  answer  so  far  as  avail- 
able is  best  stated  in  terms  of  matter  and  energy. 

Matter. — The  bodies  of  living  beings  are  composed  of  a 
few  chemical  elements,  such  as  are  common  in  soil  and 
water  ever3rwhere.  This  is  readily  determinable  by  chemi- 
cal analysis.  In  all  living  substance  there  are  nine  chemical 
elements  constantly  occurring,  three  others  (the  three  last 
named  below)  that  are  nearly  always  present,  and  a 
number  of  others  occur  here  and  there.     The  twelve  are: 

Carbon    C  Sulphur    .  .  .  .  S       Magnesium  .  .    Mg 

Hydrogen   .  .  .  H         Phosphorus   .  P       Sodium   ....      Na 

Oxygen O  Potassium.  .  .  K      Chlorine      ....  CI 

Nitrogen   .  .  .  .   N         Iron    Fe     Calcium.  ....     Ca 


THE   SIMPLER  ORGANISMS  83 

The  four  in  the  first  column,  carbon,  hydrogen,  oxygen 
and  nitrogen  coUvStitute  over  99  per  cent  of  the  Hving  sub- 
stance, the  others  being  present  in  very  small  amounts. 

In  nature  these  elements  are  found  everywhere  in  the 
crust  of  the  earth,  combined  as  simple  mineral  salts,  which, 
being  more  or  less  soluble,  are  found  also  in  the  waters  of 
the  earth.  That  these  salts  will  maintain  the  life  of  the 
green  plant  cell  may  readily  be  determined  by  supplying 
them  to  it  as  food.  The  commonly  used  food  solution  for 
green  plants  has  the  following  composition: 

Distilled  water  (H^O)    1,000.     grams 

Potassium  nitrate  (KNO^)    i. 

Sodium  chloride  (NaCl)     0.5 

Calcium  sulphate  (CaSO^)     0.5 

Magnesium  sulphate  (MgSo^) 0.5 

Potassium  phosphate  (K^HPO^)    .  .  0.5 

Ferrous  sulphate  (Fe^SO  J a  trace 

Here  we  have  all  of  the  twelve  elements  listed  above  ex- 
cept carbon,  and  this  the  green  plant  obtains  from  the  car- 
bon dioxide  (CO  J  of  the  air,  either  direct,  if  it  be  a  terrestrial 
plant,  or  dissolved  in  the  water,  if  it  be  aquatic.  On  such  a 
solution  of  the  simplest  mineral  compounds  green  plants 
thrive.  These  elements  are  recombined  in  the  living  body 
into  compounds  of  very  much  greater  variety  and  complex- 
ity, the  more  important  of  which  fall  into  two  great  classes, 
according  as  they  possess  or  lack  nitrogen  in  their  composi- 
tion: 

I.  Carbohydrates  and  fats:  non-nitrogenous  compounds, 
containing  carbon,  oxygen  and  hydrogen,  but  no  nitrogen. 

I I .  Proteins :  nitrogenous  compounds  of  great  complexity. 
These  substances,  formed  in,  and  constituting  the  bodies 

of  plants,  are  the  primary  food  of  animals. 

Energy. — The  forces  that  operate  upon  living  bodies  are 
those  that  operate  upon  the  non-living:    gravitation,  heat, 


84  GENERAL  BIOLOGY 

light,  electricity,  magnetism,  mechanical  energy,  molecular 
energy  (cohesion,  adhesion,  attraction  of  molecules)  and 
chemical  energy  (chemical  affinity,  the  attraction  of  atoms). 
In  the  living  world,  as  elsewhere,  energy  may  not  be  de- 
stroyed, but  may  be  endlessly  transformed.* 

The  primary  source  of  energy  for  living  beings  is  the  sun's 
rays.  The  radiant  energy  of  the  sun,  acting  on  the  chloro- 
phyl-bearing  protoplasm  of  the  green  plant  cell,  effects  the 
cleavage  of  carbon-dioxide  into  its  two  constituent  ele- 
ments, carbon  and  oxygen.  Then  ensues  the  synthesis  of 
the  liberated  carbon  with  water  to  form  sugar,  which  may 
be  transformed  into  starch,  and  stored  in  the  tissues.  The 
chemical  statement  of  the  reaction  (a  statement  of  the  shift 
of  the  elements  only,  that  tells  nothing  of  the  enormous 
consumption  of  energy  involved)  is,  in  its  simplest  form,  as 

follows : 

Carbon  dioxide  Water     Fruit  sugarf       Oxygen 

6  CO,     +     6H,0   =   C,H„0,     +'60, 

Thio  equation  expresses  graphically  the  primary  syn- 
thesis of  inorganic  materials  to  form  an  organic  compound. 


*Energy  may  be  either  active  {kinetic)  or  latent  {potential.) 
Kinetic  mechanical  energy  is  that  of  a  clock  spring,  moving  by  the 
release  of  tension  the  works  of  the  clock:  it  is  potential  when  the 
spring  is  wound  up,  before  the  pendulum  is  started  swinging.  Or 
it  is  that  of  a  pile  driver  hammer  falling  and  delivering  a  stroke: 
it  was  potential  when  the  hammer  was  lifted  and  ready  to  be  let 
fall.  Kinetic  chemical  energy  is  that  of  coal  burning  in  an  engine, 
moving  the  piston:  it  was  potential  in  the  coal.  It  is  that  of 
powder  exploding  in  a  gun :  it  was  potential  before  the  cap  was 
struck.  Energy  was  used  to  wind  the  clock,  to  lift  the  hammer, 
to  combine  the  unwilling  elements  of  the  powder — it  disappeared: 
it  was  rendered  latent  or  potential. 

tThe  simple  sugars  differ  from  starch  (QHjoOg)  mainly  in  that 
they  contain  relatively  more  water.  The  complex  sugars  differ  in 
being  multiples  of  the  simple  sugar  lacking  one  molecule  of  water 
for  each  molecule  of  the  simple  sugar  taken  (ordinarv^  cane  sugar, 
Cj^HjgOjj).  Through  the  series  of  carboh3^drates  (sugars,  starches, 
etc.,)  carbon  is  combined  with  hydrogen  and  oxygen,  the  two  latter 
retaining  the  ratio  they  have  in  water.     The  formula  of  the  series, 

(QHioOs)"- 


THE   SIMPLER  ORGANISMS  85 

In  order  to  understand  the  energy  involved  it  is  necessary 
to  take  into  account  the  attraction  of  the  atoms.  Carbon 
and  oxygen  have  strong  mutual  affinity,  and  combine  to- 
gether in  carbon  dioxide  to  produce  a  very  stable  compound. 
In  the  above  reaction  the  carbon  is  separated  from  the 
oxygen,  and  this  requires  the  expenditure  of  energy — the 
energy  of  the  sun.  In  overcoming  the  strong  affinity  of 
carbon  and  oxygen  for  each  other,  this  energy  disappears, 
being  rendered  potential  in  the  separated  atoms:  it  will 
reappear  in  like  amount  whenever  these  reunite.  It  is  readily 
measurable  in  terms  of  heat.  The  heat  produced  by  com- 
bining twelve  grams  of  carbon  with  thirty-two  grams  of 
oxygen  (an  ounce  and  a  half  of  these  two  elements)  is  suffi- 
cient to  raise  the  temperature  of  a  kilogram  (over  two 
pounds)  of  water  from  the  freezing  to  the  boiling  point, 
and  in  the  separation  of  like  quantities  of  these  elements 
whether  in  the  electric  furnace  or  in  the  green  leaf,  a  like 
amount  of  energy  is  rendered  potential. 

It  is  easy  to  demonstrate  that  starch  is  formed  by 
chlorophyl -bearing  protoplasm  only  in  the  presence  of  sun- 
light. It  is  not  difficult  by  proper  chemical  means  to 
determine  the  composition  of  the  sugar  or  starch  formed, 
but  it  is  impossible  to  follow  its  formation  by  direct  obser- 
vation: hence  it  must  be  borne  in  mind,  the  above  equation 
is  a  theoretical  explanation,  based  on  knowledge  of  the 
behavior  of  the  chemical  elements,  of  the  nature  of  the  com- 
pounds in  the  food  and  in  the  products  of  the  plant,  and  of 
the  observable  phenomena  of  its  nutrition.  If  so  great 
difficulties  attend  the  explanation  of  the  first  step  in  the 
synthesis  of  organic  substances,  it  will  be  readily  appreciated 
why  the  succeeding  steps  involving  the  manufacture  of 
proteins,  are  little  understood.  A  purely  theoretical  ex- 
planation of  the  production  of  asparagin,  one  of  the  simplest 
of  organic  nitrogen  compounds,  of  wide  distribution  in  green 
plants  is  that  of  the  following  equation : 


86  GENERAL  BIOLOGY 

Glucose  +  Potassium  =  Asparagin  +  Potassium  +  Water  4-  Oxy- 
nitrate  oxalate  gen 

C,H,,0,  +  2KNO3  =  C^N3N,03  +  K,C,0,  +  2Hfi  +  3O 

The  mineral  nitrates,  sulphates,  phosphates,  etc.,  enter 
into  succeeding  combinations. 

Few  proteins  have  been  successfully  analyzed;  but  it  is 
well  known  that  many  of  them  are  of  exceedingly  complex 
structure.  Their  molecules  are  composed  of  a  very  large 
number  of  atoms,  in  loose  combination.  As  the  size  of  the 
molecule  increases,  the  stability  decreases,  as  bricks  incline 
to  topple  when  piled  too  high.  A  sample  analysis  of  the 
molecule  of  a  familiar  protein,  hcemoglobin,  from  the 
blood,  gives  results  corresponding  to  the  following  formula: 

C6o»H,,„N,,,Fe,S3  0,„. 

The  reverse  process,  whereby  these  complex  and  unstable 
compounds  are  broken  up  again  into  simpler  ones  with  the 
liberation  of  their  energy  for  the  use  of  the  body,  is  even  less 
understood  in  its  details :  it  is  chiefly  known  by  its  results. 
The  end  products  of  metabolism  in  animals  are  water, 
carbon  dioxide,  urea  (CH^  N^O)  uric  acid  (C^H^N^  O^)  and 
such  other  simple  nitrogen  compounds  as  ammonia,  adenin, 
xanthin,  creatin,  etc.;  and  in  plants  they  are  the  same  ex- 
cept that  the  nitrogen  liberated  by  proteid  dissimilation  is 
recombined  and  does  not  appear  as  waste.  The  accompany- 
ing crude  diagram  is  an  attempt  to  represent  graphically  the 
relations  the  more  important  of  these  compounds  bear  to 
each  other  in  income  and  outgo  of  matter  for  organisms. 
It  is  as  the  map  of  a  country  as  yet  but  little  explored. 


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88  GENERAL    BIOLOGY 

While  the  analysis  cf  the  processes  involved  in  the  metab- 
olism of  the  living  substance  is  difficult,  and  details  are 
somewhat  uncertain  and  only  the  beginning  and  the  end 
steps  have  hitherto  been  traced,  there  is  no  doubt  whatever 
about  a  number  of  the  main  facts : 

1.  That  the  organic  life  of  the  world  is  supported  on 
water,  carbon  dioxide  and  simple  mineral  salts,  gathered 
and  assimilated  by  the  green  plant  cell. 

2.  That  these  mineral  substances  are  of  simple  composi- 
tion, are  composed  of  but  few  elements  united  strongly,  and 
that  they  are  A^ery  stable,  and  devoid  of  potential  energy. 

3.  That  the  non-nitrogenous  substances  first  combined 
under  the  power  of  the  sun's  rays,  are  compounds  of  a 
higher  order  of  complexity  of  less  stability  and  of  much 
more  potential  energy. 

4.  That  the  nitrogenous  substances  (proteins)  are  of 
great  diversity  and  of  exceeding  great  complexity  of  struc- 
ture, very  unstable,  and  of  very  high  potential  energy. 

5.  That  protoplasm  is  a  complex  substance  (not  a  single 
chemical  compound) ,  probably  a  mixture  or  combination  of 
various  proteins,  water,  etc.,  so  unstable  it  is  impossible  of 
analysis  for,  to  analyze  it  kills  it,  and  death  initiates  changes 
altering  its  composition. 

6.  That  the  primary  source  of  energy  is  the  sun,  drawn 
upon  by  the  green  plants  first ;  the  supply  for  other  organ- 
isms is  the  potential  chemical  energy  of  manufactured  carbo- 
hydrates, proteins,  and  of  free  oxygen. 

Protoplasm,  the  physical  basis  of  life,  the  living  part  of 
every  living  thing,  and  essentially  the  same  in  its  general 
properties  and  functions  in  all,  possesses  in  green  plants  the 
capacity  for  developing  chlorophyl,  through  the  agency  of 
which  the  energy  of  the  sun  can  be  utilized  in  effecting  such 
analysis  of  simple  mineral  compounds  and  such  synthesis 
of  more  complex  organic  compounds  as  result  in  the  storing 


THE   SIMPLER  ORGANISMS 


89 


up  of  a  large  amount  of  energy.  Then  the  living  substance 
acts  as  a  chemical  engine,  using  the  energy  of  these  same 
organic  compounds,  and  in  that  use,  reducing  them  again  to 
simpler  ones.     Here  as  elsewhere,  neither  matter  nor  energy 


MAX   SCHULTZE 

(1825-1874^ 

"The  father  of  modern  biology."      Physiologist;  histologist:, 

who  first  showed  that  protoplasm  is  the  common 

basis  of  plant  and  animal  life. 

is  created  or  destroyed,  but  both  are  endlessly  transformed. 
The  living  body  is  constantly  changing.  It  is  only  the  con- 
stancy of  the  stream  of  income  and  outgo  that  allows  it 
to  present  a  semblance  of  an  abiding  presence.  It  is  like 
the  chemical  engine  in  that  it  uses  fuel — the  food — whose 


90 


GENERAL    BIOLOGY 


transformation  into  gases  and  ash  liberates  energy  for  its 
work.  It  is  unlike  the  engine  in  that,  far  frombeing  a  mere 
contrivance  of  chambers  in  which  transformations  and  reac- 
tions may  occur,  it  is  itself  changed  constantly,  formed  and 
reformed,  regularly  gathered  from  and  returned  to  the 
stream. 

The  dissimilation  process  (katabolism),  whereby  the 
complex  organic  compounds  are  broken  up  into  simpler 
ones,  with  the  liberation  of  their  energy  for  use,  has  not 
hitherto  been  traced  step  by  step  in  detail:  indeed,  it  is 
even  less  understood  than  the  assimilative.  Its  results  are 
well  enough  known:  the  end  products  are  simple  com- 
pounds, CO 2,  H^O,  and  nitrogen  compounds  not  wholly 
reduced  to  the  grade  of  composition  they  had  when  first 
taken  up  from  the  water  (and  therefore,  a  little  energy  that 
they  still  retain  is  lost  to  the  body) .  Their  energy  has  re- 
appeared in  various  forms,  mechanical  movement,  bodily 
heat,  luminescence,  etc. 

From  the  chemical  side  it  therefore  appears  that  assimila- 
tion (anabolism)  is  the  process  of  separating  chemical 
affinities  and  of  storing  up  chemical  energy  in  complex 
compounds,  and  that  dissimilation  (katabolism)  is  the  pro- 
cess of  reuniting  affinities  in  stable  compounds  with  the 
liberation  of  energy  for  use. 

Plant  and  animal  differ  typically  in  the  nature  of  their 
intake  and  output  of  matter  and  energy,  and  the  main 
features  of  that  difference  are  expressed  graphically  in  the 
diagram  at  the  top  of  the  following  page. 

In  this  table  the  facts  are  of  necessity  stated  broadly. 
For  example  oxygen  is  given  off  by  the  green  plant  only 
in  the  light,  and  among  animal  foods  organic  and  inor- 
ganic materials  are  set  down  together.  The  latter  consti- 
tutes a  very  small  part  of  animal  food,  never- the-less  the 
diagram  should  aid  in  forming  a  definite  conception  of  the 
fundamental  nutritive  relations  of  plants  and  animals. 


THE   SIMPLER   ORGANISMS 


91 


Pi 

H 

< 


O 
Pi 


Income 


CO^  from 
the  air 

Mineral 
salts  in 
solution 


Outgo 


Free 
oxygen 

jCO, 
|H,0 


The  Green 

Plant 

Cell 


Radiant 

energy  of 

the  sun 

Chemical 

energy 

of  free 

oxygen 


Heat,  inove 
ments  of  pro- 
toplasm, &c. 

Chiefly  dis- 
appears in 
syntheses 
organic 
compounds, 
becoming 
potential 


of 


Income 

Free 


oxygen 


Proteins 
Carbohy- 
drates and 
fats  in  food 
H.O  &  salts 


Outgo 


CO3 
H/J 

Urea  and 

other 

nitrogen 

compounds 


The 

Animal 
Cell 


Potential 

chemical 

energy 

of  the  food 

and  of  free 

oxygen 


Movements, 
heat,  &c. 

(A  Httle  is 

lost  in 

nitrogen 

waste) 


III.       SOME    INTERMEDIATE    AND    UNDIFFERENTIATED    FORMS. 

The  typical  algae  and  protozoa  studied  thus  far,  conform 
to  our  general  notion  of  plant  and  animal,  derived  from 
contact  with  the  higher,  familiar  forms  of  life.  The  green 
color  of  the  plant  and  the  free  movement  and  foraging 
habit  of  the  animal  seem  at  first  to  mark  out  naturally  two 
distinct  groups;  among  the  higher  forms  there  is  no  diffi- 
culty about  distinguishing  between  plant  and  animal.  It 
is  easy  to  tell  a  dove  from  a  daffodil ;  it  is  not  hard  to  tell  a 
green  alga  from,  a  free  swimming  gray  protozoan ;  but  there 
are  among  the  lower  organisms  some  that  do  not  clearly 
show  even  the  broad  distinctions  of  the  preceding  diagram, 
and  some  that  so  combine  the  characters  of  the  two  groups 
that  one  may  not  say  with  assurance  whether  they  are 
plants  or  animals. 


92 


GENERAL    BIOLOGY 


We  will  first  consider  a  large  and  important  ecological 
group  of  organisms  that  we  recognize  as  plants  although  they 
do  not  contain  chlorophyl,  and  they  do  require  much  the 
same  food  as  animals;  after  that,  two  other  groups  with 
characters  so  intermediate  that  they  are  discussed  in  text 
books  of  both  botany  and  zoology  at  the  present  day. 

I.   PLANTS  THAT  LACK  CHLOROPHYL. 

The  most  important  common  characteristic  of  the  large 
ecological  group  of  organisms  we  now  come  to  consider,  is 
physiological:  lacking  chlorophyl,  they  have  abandoned 
the  primary  plant  function  of  gathering  food  m.aterials 
directly  from  the  inorganic  world.  They  must  have  organic 
food.  They  can  derive  no  energy  from  the  sun,  and  they 
thrive  often  quite  as  well  without  sunlight.  They  use  the 
same  foodstuffs  as  animals:  yet  in  structure  and  growth - 
habit  they  are  plants  very  much  like  green  species  of 
parallel  development. 

Yeasts. — These  are  unicellular  chlorophyless  plant's  of 
the  group  of  fungi.  Isolated  cells  have,  save  for  their  gray 
color,  much  the  appearance  of  single  cells  of  protococcoid 
algae.  They  have  cellulose  in  their  walls ;  their  T)rotoplasm 
is  somewhat  more  granular,  contains  minute  fat  droplets 
and  is  without  a  trace  of  chlorophyl. 

The  process  of  cell  multiplication  is  peculiar.     It  is  called 

budding  (or  gemmation).  Mi- 
nute processes  are  pushed  out 
from  the  side  of  the  cell,  and  these 
grow  up  gradually  to  full  stature, 
adhering  for  a  time  to  the  parent 
cell.  Often  the  new  cell  starts 
buds  of  its  own  before  it  is  fully 
grown  itself.     Thus   while    grow- 

development;  c,  spores, formed     •     „  „,,-^-f-1^7-  +Vip    ppllt:    pnmp    fn    "hp 
on  drying,  four  within  each  cell     mg  qUlCtly    one    CCliS    COmC    XO     DC 

^^"-  assembled   in    little     clusters    or 

families  of  cells  (torulcu),  as  shown  in  fig.  55. 


Fig.  55.  Yeast,  a,  a  single  cell 
showing  nucleus  (dark  colored), 
two  vacuoles,  and  numerous 
fat  droplets ;  b,  clusters  of  grow- 
and  budding  yeast  cells 
(torulae),  in  various  stages  of 


THE  SIMPLER  ORGANISMS  93 

A  food  solution  for  yeast  that  bears  the  name  of  the  great 
biologist,  whose  fame  rests  in  part  on  discoveries  he  made 
of  the  part  yeasts  play  in  fermentation,  is  the  following: 

Pastetir's  Solution. 
.  Water  Hp    83.76  % 

CaneSugarCj^H^Pii    15.00  " 

Ammonium  tartrate  (NH^)  ^^^Hfio  •  •  •  •  ^-^^  " 

Potassium  phosphate  K^PO^ 0.20  " 

Calcium  phosphate  Ca^  (PO^)^ 0.02 

Magnesium  sulphate  MgSO^ 0.02  " 


LOUIS  PASTEUR 

(1822-1895) 

"One   of   the  most  conspicuous  figures  of  the    nineteenth 

century."      Pioneer  student  of  fermentation,  of  disease 

germs,  etc.      His  services  to  his  country  and  to 

humanity    are    commemorated    by     Pasteur 

Institutes  for  the  treatment  of  infectious 

diseases  throughout  the  civiUzed 

world. 


94  GENERAL   BIOLOGY 

If  this  formula  be  studied  it  will  be  discerned  that  the 
chemical  compounds  of  the  food  of  yeast  are  intermediate  in 
kind  between  those  of  animals  and  those  of  green  plants. 
Some  of  the  same  mineral  salts  are  used  by  both  green  and 
colorless  plants.  The  nitrogen  is  obtained  from  a  somewhat 
more  complex  compound  in  the  latter.  Only  the  sugar  is 
properly  an  animal  food.  Proteins  such  as  animals  require 
are  wholly  lacking.  It  will  be  noted  that  there  is  carbon  in 
the  formula  aside  from  the  sugar:  the  yeast  will  live,  indeed, 
in  this  solution  if  the  sugar  be  omitted  but  its  growth  will 
then  be  very  slow.  It  will  be  noted  also  that  the  sugar  is 
present  in  very  great  excess  of  the  need  of  the  yeast  for 
carbon.  The  yeast  plant  contains  a  sugar  ferment.  It 
utilizes  only  about  one  per  cent  of  the  sugar,  and  decomposes 
the  remainder  into  carbon  dioxide  and  alcohol.  The  re- 
action of  the  fermentative  decomposition  may  be  expressed 

as  follows:  Carbon 

Su^ar  Alcohol        dioxide 

C,U\fl,  =  2C,H,0  +  2CO, 

It  is  the  production  of  these  two  by-products  that  makes 
yeast  commercially  important.  Yeast  produces  the  same 
reaction  in  the  sugars  of  cider  and  wines,  and  in  the  meta- 
morphosed starches  of  the  cereal  grains,  that  are  chiefly  used 
in  commerce  in  the  production  of  alcohol.  The  carbon 
dioxide  is  also  utilized  in  the  making  of  bread.  Yeast  is 
mixed  with  the  dough,  and,  fermenting  in  it,  evolves  the 
carbon  dioxide  gas,  which  "raises"  it,  making  it  porous, 
and  improving  its  digestibility  and  flavor. 

If  a  little  fresh  yeast  be  sown  in  a  bottle  of  Pasteur's 
solution  (or  even  in  a  15%  sugar  solution  made  wdth  tap 
water,  which  wdll  be  likely  to  contain  enough  of  the  mineral 
salts  for  considerable  growth),  and  kept  in  a  moderately 
warm  place,  within  twenty-four  hours  abundant  growth 
will  be  evidenced  by  the  increasing  turbidity  of  the  liquid, 


THE    SIMPLER    ORGANISMS 


95 


and  by  the  taste  of  the  alcohol  in  it  and  by  the  odor  of  the 
escaping  carbon  dioxide*  arising  from.  it.  It  may  be 
demonstrated  by  examination  of  a  drop  of  the  fluid  with 
the  microscope. 

Molds  and  other  fungi. — These  are  chlorophylless  plants 
of  different  organization.  They  parallel  the  filamentous 
algae  in  their  structure.  The  common  black  mold  Mucor,  is 
a  much  branched,  vacuolated  and  multinucleate  cell,  of  a 
form  recalling  the  green  felt  (Vaucheria) .  Penicillium  (figure 
56)  consists  of  branching  filaments  recalling  in  their  form 
those  of  Cladophora.  Molds  live  for  the  most  part  on  a 
more  or  less  solid  substratum  of  organic  matter  and  repro- 
duce vegetatively  by  means  of  spores  that  are  distributed 
through  the  air.  Therefore,  they  have  differentiated  into 
two  parts:  the  mycelium,  the  part  immersed  in  the  sub- 
stratum, and  concerned  with  gathering  food,  a  tangle  of 

slender  root-like  fila- 
ments; and  slender 
aerial  sporophores 
that  rise  from  the  my- 
celium at  time  of  fruit- 
ing and  bear  the  spores. 
Many  molds  feed 
upon  the  bodies  of  plants 
and  animals,  living  and 
dead,  and  upon  ma- 
terials extracted  there- 
from,   obtaining    both    their    carbon    and    their    nitrogen 


Fig.  55.  Penicillium.  a,  a  little  tuft  of  the 
mould,  as  it  appears,  growing  on  the  sur- 
face of  a  nutrient  medium ;  b,  a  bit  of  the 
same,  magnified;  s,  the  original  spore;  m, 
mycelial  filaments;  h,  sporophores,  with 
spore  clusters;  c,  one  of  the  spore  clusters. 


*A  simple  chemical  test  of  the  presence  of  CO 2  in  the  escaping 
gas  may  be  made  by  thrusting  a  glass  rod  with  a  drop  of  lime 
water  suspended  on  it  into  the  mouth  of  the  culture  bottle.  The 
calcium  oxide  (CaO)  of  which  lime  water  is  a  solution,  readily 
unites  with  free  carbon  dioxide  to  form  a  white  precipitate  of 
calcium  carbonate  CaC03  (CaO-|-C02  =  CaC03)  which  may  be  seen 
to  form  in  the  drop. 


96 


GENERAL   BIOLOGY 


from  organic  compounds.  A  few  of  them  make  galls  upon 
green  plants  (fig.  28).  Many  more  (known  as  rusts, 
blights,  mildews,  etc.)  are  destructive  pests  of  green 
plants.  But  most  of  them  are  saprophytes,  and  assist 
in  the  circulation  of  food  materials  in  the  earth  by  hasten- 
ing the  decomposition  of  the  bodies  of  dead  plants. 

The  fruiting  stages  of  the  higher  fungi  are  aggregates 
or  integrates  of  filaments,  that  rise  collectively  from 
mycelia,  and  fashion  together  parts  of  various  forms: 
spheres  in  the  puft'balls,  with  the  spores  borne  inside: 
low  cup-shaped  receptacles  in  some  of  the  disc  fungi, 
or  Ascomycetes  (fig.  57),  with  the  spores  contained  in 
cylindric  spore  sacs  (asci)  in  a  fruiting  layer  (hymenium) 
in  the  bottom  of  the  cup :  umbrella  shaped  caps  in  mush- 
rooms, with  the  spores  borne  on  the  vertical  surfaces  of  ra- 
diating lamellae  underneath  the  cap. 

Study  12.     Observations  on  cultures  of  yeast  and  molds. 

Materials  needed:  A  good  yeast  culture  in  Pasteur's 
solution.  Several  plate  cultures  of  molds  of  differ- 
ent ages  on  gelatine  (directions  for  making  plate  cultures 
will  be  found  in  any  good  laboratory,  manual  of  mycol- 
ogy or  of  bacteriology).  Young  mycelia  of  Mucor, 
in    which    streaming    of    protoplasm    may    be    observed. 

One  to  three  day  old  cul- 
tures of  Penicillium,  in  which 
the  germination  of  the  spores 
may  be  observed.  Old  Peni- 
cillium cultures,  in  which  the 
spore  clusters  may  be  studied. 
Study  in  yeast,  i)  the 
evidences  of  alcoholic  fermen- 
tation and  of  the  formation 
of     carbon     dioxide     in     the 

2)  The  details 


Fig.  57.  A  disc  fungtis  (Peziza?).  /, 
the  aerial  part  of  the  fungus,  with  a 
quarter  section  cut  out  to  show  h, 
the  hymeneum.  k,  a  bit  of  the 
hymeneum  showing,  a,  ascus.  con- 
taining spores;  n,  sterile  paraphyses, 
and  m.  sub-hymenial  tissue.  /,  a 
bit  of  the  involucre  surrounding  the  p\ilture  iar- 
hymenium.  '  J 


THE    SIMPLER    ORGANISMS  97 

of  structure  of  the  single  yeast  cell.  3)  Budding  and  the 
aggregation    of    the    yeast    cells    together    into    torulae. 

Study  in  the  molds:  i)  The  differentiation  into  my- 
celium and  sporophores;  2)  The  type  of  branching,  with  ab- 
sence of  cell  divisions  in  Mucor,  3)  The  streaming  of  the 
protoplasm  in  filaments  of  Mucor.  4)  The  germination  of 
the  spores  and  the  beginning  of  mycelia  in  Penicillium.  5) 
The  development  of  the  spore  clusters  and  of  the  arrange- 
ment of  the  spores  in  Penicillium,  and  in  any  other  fruiting 
molds  that  may  be  available. 

The  record  of  this  study  may  consist  in  simple  outline 
drawings,  and  notes  on  the  things  observed. 

Bacteria. — These  are  the  smallest  of  the  chlorophylless 
plants — indeed,  they  are  the  smallest  of  living  organisms. 
They  feed  upon  much  the  same  materials  as  do  other  fungi, 
and  while  present  nearly  everywhere,  they  are  sure  to 
abound  wherever  there  are  moist  organic  substances  in  which 
they  can  multiply.  Under  favorable  conditions  bacteria 
increase  in  numbers  with  extraordinary  rapidity.  Their 
method  of  increase  is  already  familiar — grow^th  in  size, 
followed  by  cell  division.  A  division  may  recur  every  half 
hour,  and  at  this  rate  something  like  17,000,000  individuals 
might  appear  as  the  offspring  of  a  single  one  in  the  course 
of  twenty-four  hours.  Obviously,  such  a  rate  could  not 
long  be  maintained  for  want  of  food.  Their  reproductive 
capacity,  together  with  the  readiness  with  which  they  may 
be  distributed,  give  them  an  important  place  in  the  economy 
of  nature.  They  are  nature's  chief  agency  of  decomposition 
and  decay.  They  play  a  large  role  in  restoring  spent  organic 
materials  to  circulation. 

Certain  bacteria  at  times  develop  spores.  Usually  but  a 
single  spore  is  produced  in  each  cell,  the  protoplasm  of 
which  develops  a  resistant  spore  coat  within  the  old  cell 
wall   (fig.  sSd).  The  spores  are  not  injured  by  drying,  and 


98  GENERAL  BIOLOGY 

may  be  heated  even  above  the  temperature  of  boiling 
water  without  being  killed.  They  are  readily  distributed 
everywhere  by  currents  of  air. 

Bacteria  serve  their  disintegrating  function  quite  without 
regard  to  human  interests, — spoiling  foods,  or  rotting  the 
compost  heap  to  enrich  the  soil;  souring  milk,  or  ripening 
cheese;  disintegrating  living  tissues  in  disease,  or  aiding  the 
processesof  digestion,  etc.  Although  the  study  of  bacteria  has 
been  possible  only  during  the  brief  period  that  has  elapsed 
since  the  invention  of  good  microscopes,  their  effects  have 
always  been  known,  and  many  empirical  methods  have  been 
used  for  combating  their  growth.  They  do  not  thrive  in 
acid  solutions,  hence  acids  have  long  been  used  as  a  means  of 
preserving  foods,  as  in  the  process  of  pickling  meats,  fruits, 
etc.  They  do  not  thrive  in  heavy  solutions  of  sugar,  and 
hence  jellies  and  preserves  are  composed  of  large  propor- 
tions of  sugar.  They  require  2  5  per  cent  or  more  of  water 
in  their  food  substances  for  normal  growth,  and  hence  the 
reduction  of  the  proportion  of  water  present  by  the  drying 
of  meats  and  fruits  has  long  been  practiced:  also,  the  use 
of  salt  to  make  such  water  as  is  present  unavailable.  Then 
there  are  many  substances  whose  presence  is  inimical 
to  their  growth,  which  we  now  know  as  antiseptics,  and 
which  are  the  mainstay  of  modern  surgery  (bichloride 
of  mercury,  etc.),  but  of  old,  wounds  were  forefended 
against  bacteria  by  the  pouring  in  of  oils  (such  as  turpen- 
tine)   and   of   alcoholic  solutions  (strong  wines) . 

All  these  methods,  applied  without  knowledge  of  the 
causes  of  the  evils  they  sought  to  cure,  have  been  vastly 
improved  with  the  development  of  bacteriology.  New 
processes  of  treatment  by  antiseptics,  by  sterilization,  etc., 
have  been  developed  and  old  ones  have  been  improved. 
The  bacteriologist  has  invented  transparent  culture 
media,  containing  suitable  food.     He  sterilizes  his  culture 


THE    SIMPLER    ORGANISMS 


99 


media  even  as  housewives  have  alwa3^s  sterilized  fruit  for 
canning,  sealing  while  hot ;  but  he  may  allow  time  for  the 
germination  of  any  spores  that  are  present  and  then  may 
slerilize  again;  thus  the  spores,  as  well  as  the  active  cells  of 

bacteria  are  killed.  This  is  his  method 
of  clearing  the  field.  Then  he  sows  in 
his  culture  media  the  sort  of  bacteria  he 
wishes  to  study,  and  observes  their  hab- 
its and  manner  of  growth. 

In  order  to  see  bacteria,  rather  high 
powers  of  the  compound  microscope  are 
required,  and  even  Avith  the  best  instru- 
ments little  of  internal  structure  is  vis- 
ible in  them.  There  are  three  form- 
types  commonly  found  among  them:  a) 
)     xs>     ^**^^*.        The  spherical  coccus  type,  b)  the  rod  like 

bacillus  type,  and  c)  the  spirilhmi  type 
(fig.  58).  Under  each  of  these  form 
types  many  different  species  occur, 
\vhich  may  differ  in  size  and  proportions, 
in  manner  of  grouping,  in  mode  of  cell 
division,  etc. ;  or,  different  species  may 
appear  quite  alike  to  the  eye,  and  may 
be  distinguishable  only  by  their  manner 
of  growth  in  culture  media.  By  proper 
Gtaining  methods  some  of  them  show 
locomotor  flagella,  that  are  quite  invis- 
ible unstained  (fig.  58  6  and  e). 

Certain  soil  bacteria,  of  very  great  im- 
portance to  agriculture,  cause  minute 
galls  (know^n  as  tubercles)  to  grow  upon 
the  roots  of  clover  and  other  leguminous 
plants.  These  are  important  because 
they  are  able  to  derive  their    nitrogen 


Fig.    58. 


Bacteria 


it , form  types ;  s,  coc- 
cus, t,  bacillus;  n, 
spirillum  types,  b, 
these  forms  stained, 
some  showing  flag- 
ella,   others,    none. 

c,  types  of  division; 
7;,  ordinary  cell  divi- 
sion ;  w  and  x,  simul- 
taneous division  of 
longer  filaments  in- 
to a  number  of  cells. 

d,  spore  formation 
in  different  forms,  e, 
two  species  of  bac- 
teria of  the  bacillus 
type,  showing  differ- 
ences of  appearance, 
both  stained  and  un- 
stained;  y,  the 
typhoid  baciUus;  z, 
the  bacillus  of  Asia- 
tic cholera. 


loo  GENERAL   BIOLOGY 

directly  from  the  air.  They  supply  nitrogen  to  the  clover, 
and  thus  repay  the  debt  imposed  by  the  parasitic  life. 
They  enable  the  host  plants  to  grow  upon  soils  that  are  poor 
in  nitrogen,  and  by  their  decomposition  they  leave  such 
soils  richer  than  they  found  them. 

Within  the  galls,  or  tubercles,  these  bacteria  grow 
larger  than  other  forms,  the  cells  becoming  irregularly  rod- 
shaped,  x-shaped,  y-shaped,  etc.  Hence  they  are  easily 
recognizable  with  the  microscope.  Upon  examination  of 
the  large  tubercle  we  ordinarily  find  them  filling  the  in- 
terior. Upon  the  dissolution  of  their  bodies,  their 
nitrogen  content  is  added  to  the  soil,  either  directly, 
during  the  growing  season,  or  indirectly  through  the 
intermediary  agency  of  the  clover. 

Sttidy  I  J.     A  few  observations  on  bacteria. 

Materials  needed:  A  hay  infusion  a  few  days  old;  some 
growing  clover,  or  other  leguminous  plant , bearing  root  tuber- 
cles :   a  stock  of  sterilized  culture  dishes  ready  for  sowing. 

Mount  a  little  bit  of  bacterial  jelly  from  the  surface  of  the 
hay  infusion,  and  survey  it  for  bacteria  of  the  three  form- 
types.  Look  also  for  species  of  any  type  that  may  be  dis- 
tinguishable by  size,  cell  proportions,  etc. 

Clean  some  root  tubercles,  split  open;  mount  scrapings 
from  their  interior  and  study  the  bacteria  in  them. 

Make  a  few  cultures  on  plates  of  agar  as  follows : 

1.  Seal  one  sterilized  plate  without  opening,  for  a  check. 

2.  Touch  all  your  fingertips  to  the  surface  of  the  agar 
in  a  second  plate,  cover  again,  and  set  aside  to  incubate. 

3.  AVash  the  hands  carefully  and  wipe  dry  on  a  clean 
towel,  and  repeat. 

4.  Capture  a  live  fly,  preferably  from  a  dusty  window; 
put  it  inside  a  culture  plate  and  let  it  walk  about  a  little, 
over  the  surface  of  the  gelatine  to  distribute  bacteria  from 
its  feet;   remove  the  fly  and  set  the  plate  aside  to  incubate. 


THE   SIMPLER  ORGANISMS  loi 

Watch  the  development  in  the  several  plates  and  com- 
pare results. 

The  record  of  this  study  may  consist  of  notes  and  diagrams 
of  the  things  observed. 

THE    SLIME    MOLDS. 

These  are  organisms  of  mixed  character.  In  certain 
phases  of  their  existence  they  exhibit  animal  functions;  in 
other  phases,  only  plant  functions.  In  textbooks  of 
zoology  they  are  called  Mycetozoa ;  in  most  texts  of  botany, 
Myxomycetes. 

Slime  molds  live  during  the  greater  part  of  their  life  as 
spreading  masses  of  naked  protoplasm,  which  slowly  creep 
about  through  the  tissues  of  rotten  logs,  stumps,  leaves,  etc., 
like  giant  amoebas.  They  are  soft  and  slimy  to  the  touch, 
and  are  of  a  consistency  about  like  that  of  the  white  of  an 
egg.  Their  prevailing  tints  are  yellow,  brown,  ecru  or 
purplish,  or  almost  any  color  except  green.  They  are 
usually  small,  but  with  plenty  of  food  and  moisture,  a  single 
Plasmodium  often  grows  to  be  a  foot  across.  They  shun 
the  light  and  are  always  to  be  looked  for  in  sequestered 
places.  During  nearly  the  whole  of  the  growing  season, 
from  early  summer  until  late  autumn,  they  may  be  found  in 
deep  mossy  woods,  and  in  shaded  places  by  permanent 
springs.  On  damp,  muggy  days  following  warm  summer 
showers  the  plasmodia  may  be  found,  outspread  upon  the 
surfaces  from  which  they  draw  their  nourishment.  They 
are  saprophytes.  They  feed  on  the  dissolved  organic 
substances  of  decaying  stems  and  leaves.  They  are 
always  found  associated  with  fungi  of  similar  habits,  but 
unlike  the  fungi  they  may  also  take  solid  food,  engulfing 
it  as  does  an  amoeba  by  surrounding  it  with  outflowing 
protoplasm. 

Each  Plasmodium  is  a  single  multinucleate  mass  of 
protoplasm,    without   separating    cell    walls.     The  nuclei 


I02 


GENERAL  BIOLOGY 


divide  and  become  very  numerous,  but  there  is  no  dis- 
tinction of  cells.  A  Plasmodium  may  become  divided 
by  the  flowing  apart  of  its  mass  in  divergent  direc- 
tions, or  two  Plasmodia  may  meet  and  wholly  coal- 
esce.    They  possess  little  individuality. 

Dry  weather  checks  the  growth  of  the  plasmodia  and 
often  initiates  the  reproductive  phase  of  the  life  of  the  slime 

molds,  in  which  they  re- 
semble plants.  The  plas- 
modia then  abandon  the 
darkness  and  creep  out  upon 
the  exposed  surfaces  of  the 
log  or  stump,  or  a  little  way 
up  the  stems  of  nearby 
plants.  They  develop  cell 
walls  about  all  their  nuclei 
and  these  walls  are  compos- 
ed of  a  characteristically 
vegetable  substance,  cellu- 
lose. Their  most  elevated 
portions  develop  sporangia 
of  various  and  often  beauti- 
ful forms.  These  contain 
multitudes  of  spores.  This 
maturing  process  takes  place 
Slime  molds   in  spore  bearing   very    Quickly — a    few  days 

a,  irichia;  o,  btemomtis.  j         i.  j  j 

or  even  hours  may  be 
sufficient ;  it  is  to  be  sought  on  the  bright  and  sunshiny  days 
that  follow  summer  show^ers. 

The  spores  are  scattered  with  the  bursting  of  the  spor- 
angia at  maturity.  In  some  of  the  commoner  slime  molds 
(fi§^-  59)  >  they  are  assisted  in  making  their  exit  by  the 
movements  of  certain  spirally  twisted  threads  {capillitial 
threads:    collectively  the  capillitium)  which    occur   in  the 


Fig.  59. 
stage. 


THE    SIMPLER     ORGANISMS 


103 


sporangia  with  them.  These  threads,  formed  from  residua] 
shreds  of  the  plasmodium,  are  very  hydroscopic,  and  when 
they  dry  out,  twist  and  turn  vigorously,  scattering  the 
spores.  When  favoring  wind  or  water  bears  a  spore  to  a 
favorable  place  for  germination,  it  bursts  its  cell  wall  and 
there  creeps  out  therefrom  a  minute,  naked  amoeboid  cell, 
which  moves  about  for  a  time  by  means  of  pseudopodia. 
Then  it  develops  a  long  lash  at  one  end  of  the  body  (fig.  60) 
with  the  aid  of  which  it  swims  for  a  season.  Then  it  settles 
down,  in  company  with  others  of  like  kind,  and  with  the 
others  fuses  into  a  plasmodium  of  minute  size,  which  has 
only  to  absorb  food  and  grow  to  attain  to  the  size  and 
character  of  that  with  which  we  started. 

Thus  we  see  that  from  the  time  of  germination  of  the  spore 


=^    #     U 

Fig.  60.  Reproduction  in  slime  molds,  a,  elater;  b,  spores; 
c,  one  germinating  spore  and  three  amoeboid  cells  escaped 
from  other  spores;  d,  the  same  cells  a  little  later  when  free 
swimming;  e,  convergence  of  these  cells  to  form  a  Plasmo- 
dium ;  /,  a  small  plasmodium. 

until  the  plasmodium  is  mature,  the  slime  mold  exhibits 
the  free  locomotion  and  the  feeding  habits  of  the  animal, 
while  thereafter  it  develops  cellulose  cell  walls  and  pro- 
duces spores  like  a  plant.  Nature  has  not  always  estab- 
lished hard  and  fast  boundaries,  even  between  her  major 
groups  of  organism. 

Study  14.    Observations  on  slime  molds. 

Materials  needed:  living  plasmodia,  and  mature  spor- 
angia of  any  common  species.  Both  may  be  brought  into 
the  laboratory  on  pieces  of  moist  wood.  The  plasmodia,  if 
broken  into  fragments  with  the  wood,  and  placed  on  slides 
under  a  darkened  bell  jar,  will  in  a  few  hours  creep  off  the 


I04  GENERAL    BIOLOG  7 

wood  on  to  the  slides,  and,  being  thus  well  spread  out,  and 
freed  from  dirt,  will  show  the  streaming  movements  of 
protoplasm  beautifully.  One  may  be  fixed  on  the  slide 
with  strong  alcohol  and  stained  with  safranin  to  demon- 
strate the  many  nuclei.  If  an  inclined  slide  be  placed 
against  the  edge  of  a  plasmodium  and  a  gentle  current  of 
water  made  to  run  down  the  slide,  the  plasmodium  will 
creep  up  the  slide  in  opposition  to  the  current. 

Plasmodia  may  be  grown  from  spores  at  any  season,  Ly 
sowing  the  spores  upon  a  proper  nutrient  surface  and  keep- 
ing them  moist  and  under  a  darkened  bell  jar. 

The  things  that  may  most  profitably  be  studied  are: 
i)   In  the  living  plasmodium,  its  movements,  its  struc- 
ture, its  engulfing  of  solid  bits  of  food  (such  as  mushroom 
fragments),  its  protoplasmic  currents  and  its  reactions  to 
stimuli. 

2)  In  its  fruiting  phase,  the  form  and  structure  and  group- 
ings of  the  sporangia,  the  spores  and  their  structure,  and 
the  capillitial  threads  or  other  sterile  parts  in  the  sporan- 
gium. 

3)  In  the  development  of  the  spores,  the  first  amoeboid 
stage,  the  later  free-swimming  stage,  and  the  fusion  of  cells 
to  form  minute  new  plasmodia  (all  of  which  may  be  seen  in 
drop  cultures,  made  as  directed  in  the  appendix). 

The  record  of  this  study  may  consist  of  sketches  and 
diagrams  of  the  things  observed. 

THE    FLAGELLATES. 

Unlike  the  slime-molds,  the  flagellates  are  minute 
organisms  having  considerable  definiteness  of  body  struc- 
tures, yet  they  have  not  clearly  and  uniformly  differen- 
tiated plant  and  animal  characteristics.  Hence  these  also, 
or  at  least  a  considerable  part  of  them,  are  treated  in  books 
on  both  botany  and  zoology;    in  the  former  being  ranked 


THE  SIMPLER  ORGANISMS  105 

with  the  protococcoid  algae,  in  the  latter  with  the  masti- 
gophorous  protozoa. 

Euglena  is  a  common  flagellate  that  will  serve  for  intro- 
duction to  the  group.     It  abounds  in  sluggish  waters,  and  if 

a  quantity  of  trash  and  bottom 
silt  be  placed  in  a  large  glass  jar 
and  allowed  to  stand  awhile,  Eu- 
FiG.  61.    Euglena.    n, nucleus;      glcua  will  usually  be  fouud  swim- 

m,     mouth;    cv,     contractile  .  .  ^  ,      ,1  r 

vacuoiewith  pigment  fleck,  p,      mmg  m  nuniDcrs  at  the  suriace 

beside  it; ^,  flagellum.  ,  .,  j.     j_u        i-    t-j.         rr 

on  the  side  next  the  light.  It 
abundant  it  will  be  very  evident  by  its  bright  green  color. 
It  may  form  a  green  film  on  the  surface  visible  to  the 
unaided  eye. 

If  a  drop  from  this  film  be  mounted  for  the  microscope 
and  examined  one  sees  as  soon  as  he  finds  the  organisms 
that  they  exhibit  the  bright  green  chlorophyl  color  of  the 
algae  along  with  the  active  swimming  movements  of  very 
lively  protozoans.  The  swimming  is  rapid,  and  at  first  it 
may  be  difficult  to  keep  a  single  individual  in  the  field  of 
observation.  It  is  jerky,  too ;  not  the  regular  and  orderly 
progression  of  a  ciliate,  but  quick  movements  from  side  to 
side,  due  to  the  lashing  of  the  long  flagellum  at  the  anterior 
end  of  the  body  (see  fig.  6 1) . 

In  an  individual  that  has  settled  to  creeping  about  on  the 
slide  one  may  observe  the  form  of  the  body — oval,  blunt  in 
front  and  pointed  at  the  rear,  showing  a  transparent 
ectosarc,  and  an  endosarc  filled  more  or  less  completely  with 
green  chlorophyl,  and  containing  near  the  front  end  a 
pigment  fleck  of  more  or  less  orange  color.  The  flag- 
ellum may  be  seen  to  be  as  long  as,  or  lor.ger  than  the 
body.  It  may  be  broken  off,  however,  and  if  present  it  is 
so  transparent  it  can  only  be  seen  in  very  favorable  light, 
or  sometimes,  only  after  staining.  Beside  its  base  is  a 
cleft — a   rudimentary  mouth — a  receptacle   for  solid    food 


io6 


GENERAL  BIOLOGY 


— another  animal  character.  In  the  midst,  more  or  less 
hidden  by  the  chlorophyl  and  by  engulfed  foods,  is  the  nu- 
cleus. Reproduction  is  by  fission,  which,  also  may  be  ob- 
served in  favorable  specimens. 

Fig  62  Two  shell-  Ccratium  is  a  frcc-swimming 
^'Srltium^'anY^:  Aagcllate  which  secretes  a 
Peridinium.  spinous   shcU  that  is  probably 

a  protection  against  the  attack  of  some  of  the 
predaceous  animals  of  its  environment  (fig.  62). 
Dinobryon  is  a  colonial  flagellate  which 
develops  an  urn-shaped  membranous  shell 
open  at  the  anterior  end:  two  flagella  of  un- 
equal length  project  from  the  opening;  the 
chlorophyl  is  distributed  (fig.  63^)  in  two 
elongate  tracts  within  the  body,  and  is  somewhat 
obscured,  as  in  many  other  flagellates,  by  a 
yellowish  pigment. 

Upon  division,  one  of  the  resulting 
daughter  cells  slips  out  to  the  rim  of  the 
urn-shaped  shell,  and  secretes  for  itself  r^ 
a  new  shell  of  like  form,  attached  at  the 
base  within  the  margin  of  the  old  one. 
Repeated  divisions  thus  give  rise  to 
branched  colonies.  These  go  swimming 
about  in  the  water  in  a  most  absurd 
fashion — a  contradiction  to  all  the 
mechanics  of  submarine  navigation — the 
open  end  forward,  as  it  must  needs  be, 
owing  to  the  position  of  mouth  and 
flagella. 

Gonium  is  a  colonial  flagellate  of  very 
different  form — 16-celled  when  the  col- 
ony is  grown,  in  a  flat  raft,  four  central 
cells      destitute  of   flagella,  and    twelve 


Fig.  63.  A  colonial 
flagellate,  Dinobry- 
on. c,  a  colony;  d, 
a  portion  of  the 
same  more  enlarg- 
ed; e,  single  individ- 
ual. 


THE   SIMPLER   ORGANISMS 


107 


marginal  cells  (three  on  each  side)  with  flagella.     The  cells 
all    have    rather    thick    cellulose    walls,   and    there    is    a 

common  gelatinous  envelope  investing  the 
entire  colony.  The  motion  is  that  of  a 
whirling  disk. 

Pandorina  (fig.  64)  is  a  small  spherical 
colony  of  bi-flagellate  cells.  Usually  there 
are  sixteen  (sometimes  only  eight,  more 
rarely,  thirty-two)  of  the  cells,  closely  held 
together  in  a  gelatinous  envelope.  New 
colonies  are  formed  in  two  ways:  i)  repeat- 
ed divisions  within  the  old  cell  wall  give 
rise  to  new  colonies,  which  escape  as  colo- 
nies and  not  as  single  cells  (fig.  64  i).  2) 
each  cell  of  a  colony  may  divide  four  or  five 
times,  giving  rise  to  sixteen  or  to  thirty - 
two  cells  (sex  cells,  or  gametes)  which  es- 
cape singly  and  fuse  in  pairs,  forming 
zygotes  (fig.  64/).  Each  zygote,  later,  by 
successive  divisions  gives  rise  to  the  normal 
colony. 

Volvox  is  a  spherical  colony  of  somewhat 
similar  cells  (fig.  65).  It  grows  to  large 
size,  being  easily  visible  to  the  unaid- 
ed eye,  and  it  may  contain  hundreds  or  even  thousands  of 
constituent  cells,  all  embedded  in  the  common  gelatinous 
matrix,  their  flagella  radially  protruded  and  lashing  in  uni- 
son to  produce  a  rolling  motion.  Volvox  presents  a  remark- 
able differentiation  into  vegetative  and  reproductive  cells, 
to  be  discussed  under  a  subsequent  heading. 


WM^f 


Fig.  64.  A  colo- 
nial  flagellate 
Pandorina.  h, 
a  normal  spheri- 
cal colony ;  i, 
daughter  colon- 
ies developing 
within  the  cell 
walls  of  the  moth 
er  colony;  /, 
zygote  resulting 
from  the  fusion 
of  the  gametes; 
^, gamete;  these 
are  often  of  un- 
equal size. 


Study  ij.     A  comparative  examination  of  common  -flagellates. 

Materials    needed:     Living    specimens    of  a  variety    of 
simple    and   colonial    flagellates.     Some  of  these  will    be 


io8 


GENERAL  BIOLOGY 


obtained  by  the  method  suggested  for  obtaining 
Euglena.  More  may  be  gotten  from  the  surface 
plankton  of  shallow  ponds  with  a  towing  net  of  fine  silk  bolt- 
ing cloth.  It  being  impossible  to  say  what  forms  may  be 
found  at  any  time  and  place,  no  detailed  outline  can  be 


Fig.  65.  Volvox  (from  West,  after  Klein).  The  individual  cells 
are  united  by  radiating  strands  of  protoplasm.  A,  a  mature 
colony;  a,  spermaries;  g,  ovaries.  B,  zj'gote  resulting  from 
the  fusion  of  the  gametes,     C,  two  sperms      D,  egg. 

given  for  the  study  of  them.  Suffice  it  to  say  that  the 
flagellates  available  should  be  compared  as  to  form  and  activ- 
ities, the  manner  of  cell  aggregation  in  colonial  forms,  and 
differentiation  of  cells  in  the  colony.  And  the  individual 
cell  should  be  studied  as  to  its  covering,  the  number,  length 


THE  SIMPLER  ORGANISMS  109 

and  insertion  of  its  flagella,  the  distribution  of  the  chloro- 
phyl  and  location  of  the  pigment  spot,  position  of  the 
mouth  if  present,  etc.,  etc. 

The  record  of  this  study  may  well  consist  in  sketches, 
and  notes  on  the  things  observed. 

REPRODUCTION  AMONG  THE  SIMPLER  ORGANISMS. 

I.  Cell  division. — Increase  of  individuals  is  brought 
about  among  the  simpler  organisms,  as  we  have  already  seen, 
by  simple  c-ell  division,  or  fission.  This  process  seems  ordi- 
narily to  be  initiated  by  the  nucleus  (which  undergoes 
changes  to  be  described  in  a  subsequent  chapter)  which 
separates  itself  into  two  parts,  about  which  the  other  cell 
constituents  become  aggregated.  The  living  substance  of 
the  mother  cell  thus  lives  on  in  the  two  daughter  cells. 

Cell  division  is  an  automatic,  internal,  spontaneous  proc- 
ess. It  cannot  be  effected  artificially;  it  cannot  be  com- 
pelled or  prcA^ented.  If  a  cell  be  cut  in  two,  the  part  of  it 
containing  the  nucleus  and  a  part  of  the  cytoplasm  may 
live,  but  the  cytoplasm  deprived  of  the  nucleus  dies,  and  a 
wholly  isolated  nucleus  dies  also.  The  cell  is  the  unit  of 
organic  structure  and  function,  and  in  it  nucleus  and 
cytoplasm  bear  relations  of  mutual  dependence.  They 
work  together  in  both  nutritiA^e  and  reproductive  processes. 

Cell  division  results  from  growth,  the  increase  of  size  dis- 
turbing the  nutritive  relations  between  the  living  substance 
and  its  food  supply :  for  volume  tends  to  increase  faster  than 
surface ;  the  former  (if  the  cell  be  spherical)  as  the  cube, 
the  latter  as  the  square  of  the  diameter.  Therefore,  the 
mass  of  protoplasm  tends  to  increase  more  rapidly  than 
the  surface  through  which  it  derives  its  nourishment  and 
expels  its  waste.  This  is  a  sufficient  reason  why  cells  are 
small,  and  why,  when  a  standard  maximum  size  is  reached, 
fission  sets  in  to  keep  them  so. 


no 


GFNERAL  BIOLOGY 


For  every  kind  of  cell  there  is  a  normal  size,  which  being 
attained,  nucleus  and  cytoplasm  act  conjointly  to  bring 
about  a  separationof  the  cell  body  into  two  equal  parts,  and 
to  perpetuate  in  each  of  the  descendant  cells  the  substance 
and  the  characters  inherited  from  past  cell  generations. 

When  cells  after  division  remain  in  contact  they  tend  to 
form  individuals  of  a  higher  order.  These  may  be  merely 
colonies  of  loosely  associated  and  physiologically  independ- 
ent cells — mere  aggregates — or,  if  the  cells  become  inti- 
mately associated  in  relations  of  mutual  dependence,  then 
each  aggregate  becomes  a  unit  organism.  In  organisms  of 
this  compound  sort  new  individuals  may  be  formed  by 
external  agencies.  The  filament  of  Spirogyra,  for  instance, 
may  be  broken  into  a  number  of  parts,  and  each  part,  pro- 
vided it  contain  an  uninjured  cell,  may  become  a  new  fila- 
ment. New  individuals  of  such 
branching  types  as  Cladophora  or 
Dinobryon  are  formed  when  the 
older  parts  connecting  branches  to- 
gether meet  v/ith  accident  or  death 
and  the  connection  is  dissolved. 
These  are  negative  processes,  that 
do  not  account  for  the  producti  n  of 
anything  new;  it  should  be  clearly 
recognized  that  cell  division  is  the 
universal  mode  of  increase  among 


organisms. 


Fig.  66.  Cercomonas  (in  part 
after  Dallinger).  a,  divi- 
sion; b,  a  normal  individual; 
c,  an  individual  approach- 
ing the  time  for  conjuga- 
tion; d  the  begnning  of  con- 
jugation; e,  end  of  conjuga- 
tion and  fusion  of  nuclei. 


2.  Sexual     reproduction. — In     a 

few  minor  groups  of  the  smaller 
organisms,  cell  division  goes  on  un- 
interruptedly, and  is  the  only 
known  phenomenon  of  reproduc- 
tion; but  in  all  the  larger  and 
higher  forms  of  life  (and  in  so 
many  of  the  simpler  ones  also  that 


THE  SIMPLER   ORGANISMS  in 

it  is  well  nigh  universal)  another  phenomenon  known 
as  conjugation  or  sexual  reproduction  enters  in 
periodically,  alternating  with  long  periods  of  cell 
division.  This  process  consists  in  the  fusion  of  two  cells, 
and  so,  is  the  reverse  of  cell  multiplication.  Like  cell 
division,  it  is  an  automatic  spontaneous  act  of  the  cells 
themselves,  that  cannnot  be  artificially  performed.  It  oc- 
curs after  a  long  period  of  cell  division  (after  more  than  loo 
generations  of  cells  produced  by  fission  in  Paramoecium, 
according  to  Maupas),  and  it  seems  to  follow  a  decline  in 
vegetative  vigor.  This  is  indicated  by  the  loose  am.oeboid 
form  taken  on  by  certain  shapely  flagellates  (fig.  66)  just 
previous  to  conjugation.  It  is  followed  by  restoration  of 
the  normal  form,  and  by  renewed  activity  in  cell  division, 
therefore,  it  seems  to  be  a  sort  of  rejuvenating  process. 

It  introduces  into  cell  lineage  new  influences  from  with- 
out, by  commingling  the  substance  of  two  cells  that  are  of 
diverse  ancestry  and  that  have  lived  apart  under  difi'erent 
influences. 

This  fusion  may  occur  among  the  simpler  organisms  in  a 
great  variety  of  ways.  It  may  be  temporary  and  partial  as 
in   Paramoecium.     Two   individuals    come     together    and 

partially    fuse    at    the    anterior 

Fig.    67.     Diagram  il-  .,         rr^.      .  .,    .        - 

lustrating    conjuga-    cnd.      i  hcir  meganuclci    degen- 

tion     between     two  ,  ,,      .  .  -    .  ., . 

cells  of  ciosterium;    cratc ;     their      micronuclei      di- 

y,    the      empty    and         .  -,  <         r  i  • 

discarded  cell  walls;    Vide;    a  part   ot  cach  micronu- 

z,  the  zygospore,    or        -•  •     j        ,  ^  ^  t 

zygote,    resulting     ClcUS   paSSCS    OVCr    lUtO    thc   OthCf 
from  conjugation.  -r-.  •  .        r  • .  ■, 

Paramoecium  to  tuse  with  a  cor- 
responding part  of  the  micro- 
nucleus  of  that  animal,  the  two  together  forming  the  new 
micronucleus.  The  two  paramoecia,  after  this  exchange 
of  substance  separate,  and  enter  upon  another  period  of  in- 
crease by  fission. 

More  often  the  fusion  is  total  and  permanent.  It  may  be  be- 
tween cells  that  are  of  normal  size  and  equal  activity ,  (fig.  67) 


112  GENERAL   BIOLOGY 

as  in  Closterium.  Spiroyra  shows  the  slight  difference 
that  one  of  its  conjugating  cells  is  slightly  more  active,  its 
protoplasm  passing  over  bodily  into  the  other 
one.  In  Epistylis  (fig.  54)  there  is  greater  difference  in 
size  and  the  active  cell  possesseslocomotory  apparatus  and 
is  free-swimming. 

It  may  occur  between  cells  of  reduced  size,  such  as  the 
swarm  spores  of  the  Sporozoa,  next  to  be  studied  (fig.  68). 
But  it  usually  occurs,  even  among  the  simpler  organisms, 
between  two  specialized  reproductive  cells  (gametes)  of 
opposite  character: 

SPERM  small —  active  — with  little  cytoplasm 
(or  spermatozoan)  and  no  inclusions. 

EGG  large — -receptive — cytoplasm  charged  with 
(or  ovunt)  food  materials. 

This  alone  is  sexual  reproduction,  since  in  absence  of  this 
differentiation  there  is  no  sex.  Sex  cells  are  well  illustrated 
in  Volvox.  The  many  generations  of  cells  produced  by 
fission  remain  in  contact  and  constitute  the  spherical  colony. 
A  few  scattered  cells  in  the  colony  cease  their  vegetative 
activity  and  become  differentiated  in  two  ways.  Some  of 
them  repeatedly  divide  until  very  small,  develop  swimming 
flagella,  and  are  liberated  as  free-swimming  sperms.  The 
others  increase  in  size  and  food  content  by  storing  up  in 
their  cytoplasm  food  materials  derived  from  neighboring 
cells,  and  become  eggs.  At  maturity  the  sperms  break  out 
and  swim  abroad.  The  egg  remains  where  produced,  and 
develops  only  if  some  wandering  sperm  find  it  and  fuse 
with  it.  After  such  fusion  (fertilization) ,  ordinary  cell  divi- 
sion begins  again;  and  the  little  cluster  of  cells  soon  formed 
is  set  free  as  a  new  minute  volvox  colony. 

The  case  of  Volvox  is  especially  significant  because  Volvox 
is  like  all  the  higher  organisms  in  the  possession  of  true  sex 


THE   SIMPLER  ORGANISMS  113 

cells.  The  stoneworts,  Chara  (fig.  48)  and  Nitclla,  show  the 
same  phenomena,  with  eggs  and  sperms  developed  within 
much  more  highly  specialized  chambers  (ovary  and  sper- 
mary  respectively) .  In  the  other  forms  we  have  been  con- 
sidering any  cell  might  enter  into  conjugation.  But  here, 
the  greater  part  of  the  cells  of  the  body  (bodyplasm)  eat 
and  grow  and  die  without  descendants,  and  only  the  few 
that  are  relieved  of  nutritive  functions  and  wSet  apart  for 
reproduction,  live  on  in  succeeding  generations. 

Among  the  parasitic  protozoans  (Order  Sporozoa)  there 
are  many  concurrent  modifications  of  life  history  and  of 
reproductive  methods.  One  of  the  most  instructive  of  these 
is  the  common  gregarine  that  lives  parasitically  in  the 
stomach  of  grasshoppers  and  crickets,  where  it  is  usually 
found  abundantly  in  summer  and  autumn.  It  is  a  large 
protozoan  when  grown,  easily  recognizable  with  the  un- 
aided eye,  of  a  yellowish  color,  and  often  so  abundant  that 
when  a  grasshopper's  stomach  is  opened  it  looks  as  if 
lined  with  a  layer  of  yellow  corn  meal.  Each  minute  grain 
of  the  apparent  meal  represents  a  single  gregarine,  or  a  pair 
of  gregarines  in  apposition  (fig.  68). 

The  body  of  this  gregarine  shows  a  constriction  across 
one  end  which  simulates  the  division  between  cells;  but 
on  closer  examination  a  nucleus  is  found  only  in  the  larger 
end.  The  cytoplasm  is  very  densely  granular,  in  so 
much  that  the  nucleus  appears  as  a  clear  spot  in  the 
midst  of  it.  The  ectosarc  is  thick,  and  is  differentiated 
into  layers,  the  outermost  of  which  is  protective  against  the 
digestive  fluids  with  which  it  is  always  in  contact  There 
are  no  locomotor  appendages — only  some  contractile 
fibres  developed  in  the  ectosarc,  admitting  of  slow 
movements  of  the  body. 

These  gregarines  begin  life  in  the  grasshopper's  stomach 
(when    swallowed  with  the  food)    as    exceedingly  minute 


114 


GENERAL  BIOLOGY 


bits  of  hyaline  protoplasmic  cells.  Each  develops  an 
organ  for  the  penetration  of  the  wall  and  attachment  to  a 
single  digestive  cell,  from  which,  during   the  early  part  of 

its  life  it  draws  its  nourishment. 
Later  it  becomes  free,  and  grows 
enormously,  without  dividing.  As  it 
increases  in  size  its  endosarc  be- 
comes charged  with  an  abundance  of 
absorbed  food  materials,  and  takes 
on  the  dark  and  granular  appearance 
already  noted. 

This  long  period  of  growth  and 
accumulation  of  food  materials  is 
followed  by  one  of  rapid  and  exten- 
sive cell  division  outside  the  body  of 
the  grasshopper.  Late  in  the  season, 
when  the  grasshoppers  and  crickets 
also  are  old,  most  of  the  gregarines 
are  found  attached  end  to  end  in 
pairs.  This  looks  like  conjugation 
at  first  sight  and  has  been  so  inter- 
pretisd  in  the  past;  but  it  is  only  ap- 
position, preparatory  to  further  de- 
velopment. In  such  pairs,  the  pro- 
toplasm will  often  show  a  different 
appearance  in  the  two  individuals. 
One  cell  of  the  pair  divides  into  a 
very  large  number  of  motile  sperm 
cells,  the  other  into  a  smaller  number 
of  egg  cells :  the  separating  walls  be- 
tween become  dissolved  and  eggs  and  sperms  are  comming- 
led in  the  common  interior,  and  fuse  in  pairs. 

Each  of  the  fertilized  eggs  divides  three  times  into  eight 
minute  cells  which  take  on  an  elongate  and  somewhat  boat- 


b    ^^^ 

Fig.  68.  Gregarine  from 
the  stomach  of  a  grass- 
hopper, a,  a  single  in- 
dividual, showing  the 
dense  granularity  of  the 
protoplasm;  b,  a  group 
of  individuals,  apposed 
mostly  iti  pairs,  as  they 
appear  previous  to  sex 
cell  formation. 


THE   SIMPLER   ORGANISMS  115 

shaped  form  (whence  they  are  called  pseudo-navicellae)  and 
these  are  liberated  by  the  rupturing  of  the  containing  wall. 
The  spores  are  scattered  among  the  herbage  and  may 
readily  be  eaten  by  another  grasshopper  in  the  spring; 
and  if  so  fortunate  (for  therein  lies  their  only  chance  of 
further  development) ,  they  repeat  the  cycle  just  outlined. 

The  deviations  from  the  normal  course  of  protozoan  life 
in  gregarines  seems  to  be  due  to  their  peculiar  parasitic 
habits.  A  long  period  of  uninterrupted  growth  is  followed 
by  rapid  and  extensive  cell  division,  reducing  the  size  again, 
first  to  that  of  normal  gametes,  and  after  fertilization, 
reducing  it  again  to  that  of  the  spores.) 

Study  16.    Observations  on  reproduction  among  the  simpler 

organisms. 

Materials  needed:  For  fusion  between  cells  of  ordinary 
size,  conjugating  Spirogyra,  or  any  of  the  Conjugatae 
among  the  algae,  fresh  or  preserved  (temporary  and  partial 
conjugation  may  often  be  seen  in  Paramoecium  and  its  allies 
among  the  ciliate  protozoans,  but  the  details  are  not  easily 
followed  by  a  beginner) . 

For  gametes,  one  of  which  is  of  moderately  reduced  size 
and  of  increased  activity,  preserved  material  in  Vorticel- 
lidae,  or, 'better,  in  any  of  the  algae,  among  which  this  is  of 
frequent  occurrence. 

For  fusion  between  cells  both  of  which  are  of  greatly 
reduced  size,  fresh  and  preserved  gregarine  material.  For 
fresh  material,  up  to  the  beginning  of  the  dividing  process, 
open  the  stomachs  of  freshly  collected  grasshoppers  (the 
head  may  be  snipped  off:  the  body  wall  slit  open;  the  ali- 
mentary canal  lifted  out  entire  and  freed  from  extraneous 
organs  and  fat,  the  stomach  wall,  opened  by  a  longitudinal 
slit,  either  with  fine  scissors  or  with  a  very  sharp  scalpel: 
the  walls  will  open  by  the  contraction  of  their  own  muscles, 


ii6  GENERAL   BIOLOGY 

and  fully  expose  the  yellow  gregarines  to  view:  these  may 
be  lifted  with  a  pipette  and  mounted  in  normal  salt  solution 
for  study) .  For  the  division,  conjugation,  and  spore  forming 
stages,  use  prepared  slides. 

For  the  ordinary  process  of  sexual  reproduction,  either 
fresh  or  preserved  material  representing  that  phase  in  either 
Volvox  or  a  stone  wort,  (Chara  or  Nitella). 

The  record  of  this  study  may  well  consist  of  drawings 
illustrating  such  phenomena  as  have  been  available  for 
study. 


CHAPTER  III 

ORGAXIC   EVOLUTIOX 

It  is  a  matter  of  common  observation  that  the  character- 
istics of  plants  and  animals  are  plastic,  and  more  or  less 
responsive  to  conditions  about  them.  We  all  know  this  to 
be  true  of  individuals.  One  familiar  with  the  breeding  of 
plants  and  animals  knows  it  is  also  true  of  species.  How 
great  the  changes,  that  may  be  wrought  in  a  compara- 
tively short  time  is  shown  by  every  cultivated  species  of 
plant  or  animal.  That  comparable  changes  are  wrought  in 
nature,  only  less  rapidly,  and  that  the  main  trend  of  the 
change  has  been  toward  higher  organization,  has  long  been 
thought,  and  is  now  generally  believed.  This  is  evolution. 
It  means  "descent  with  modification."  Forms  now  existing 
differ  from  their  remote  progenitors.  The  complex  struc- 
tures and  relations  of  the  present  day  have  developed  out  of 
the  simpler  ones  that  have  existed  in  the  past,  and  the  his- 
tory of  that  development  is  a  proper  subject  for  investiga- 
tion, being  traceable  in  the  constitution  of  the  living,  and  in 
the  remains  of  extinct  forms  of  life. 

In  this  chapter,  in  taking  up  for  brief  consideration  the 
higher  plants  and  animals,  we  shall  study  them  in  series, 
beginning  with  the  simpler  among  them.  This  is  the  logical 
order,  the  order  which  we  follow  in  all  our  studies.  It  is 
also  the  genetic  order,  the  order  of  departure  from  primitive 
conditions,  the  order  of  the  appearance  of  the  respective 
groups  upon  the  earth.  AVe  shall  see  the  nature  of  the  evi- 
dence of  their  kinship,  while  seeing  the  nature  of  the  plants 
and  animals  about  which  we  wish  to  learn. 


Ti8  GENERAL   BIOLOGY 

There  are  but  two  main  groups  of  organisms — plants 
and  animals.  If  these  are  not  always  sharply  distinguished 
among  the  lower  organisms,  they  are  distinct  enough  among 
the  higher  ones.  Our  study  is  therefore,  of  two  series  of 
forms,  which  we  shall  illustrate  in  the  fewest  possible  types 
that  will  serve  to  show  the  more  important  features  of 
their  structure  and  development.  Matters  of  function 
and  of  relation  to  environment  will  for  the  present  be  left 
largely  in  abeyance,  while  attention  is  fixed  on  the  form 
and  relations  of  the  types  in  each  series. 

I.       THE    PLANT    SERIES. 

The  briefest  admissable  classification  of  plants  is  the 
familiar  one  that  assembles  algae  and  fungi  into  one  group, 
and  makes  of  the  remaining  plants  three  groups  that  are 
somewhat  more  homogeneous  and  consistent,  as  follows: 

1.  Thallophytes;   algae  and  fungi. 

2.  Bryophytes;    liverworts  and  mosses. 

3.  Pteridophytes;  ferns,  etc. 

4.  Spermatophytes;   the  seed  plants. 

We  have  already  studied  a  few  representative  Thallo- 
phytes ;  we  shall  now  briefly  examine  a  few  representatives 
of  each  of  the  three  other  groups, 

Bryophytes:     Liverworts  and  Mosses. 

This  is  a  group  of  comparatively  small  plants,  of  very  great 
diversity  in  appearance.  Those  that  live  in  the  drier  situa- 
tions, and  that  are  more  familiar  to  us,  are  mainly  mosses; 
but  liverworts  are  common  also  in  their  proper  haunts;  in 
the  moist  shaded  places  of  deep  woods;  on  wet  rocks  by 
streams. 

Conocephalus  (fig.  69)  is  a  good  form  with  which  to 
begin  our  study  of  the  group.  The  plant  body  is  a  broad 
flat  thallus,  which  spreads  over  and  attaches  itself  closely 


ORGANIC  EVOLUTION 


119 


to  the  soil.  It  is  of  bright  green  color,  and  has  a  peculiar, 
and  seemingly  incongruous  musty  odor.  It  grows  apically, 
in  a  zig-zag  course,  dichotomously  branching  alternately 
to  right  and  to  left,  the  branches  and  parent  stem  being 
of  equal  breadth. 

If  we  tear  up  a  little  strip  of  the  thallus  from  the  soil,  we 
shall  observe  at  once  a  considerable  number  of  parts  not  seen 
among  the  algae.     First,   there  is  a  multitude  of  slender 


Fig    69.      Photographs  of  the  liverwort  Conocephalus;   the  larger  figure  is  an  enlarge"!  top 
view  of  the  thallus;  the  smaller  one,  a  side  view  of  an  old  specimen  bearing  sporophytes. 

white  rhizoids,  holding  the  plant  body  fast  to  the  soil. 
These  are  feeding  organs.  A  number  of  algae  (for  example, 
Chara,  and  Nitella)  have  similar  organs  for  attachment,  but 
they  are  much  less  developed  and  have  no  feeding  function. 
In  the  liverwort,  as  in  most  of  the  higher  plants,  rhizoids 
•  are  the  chief  means  of  taking  up  dissolved  mineral  sub- 
stances out  of  the  soil.  The  torn  end  of  the  thallus  will 
show,  also,  that  the  plant  body  is  covered  with  a  dry  surface 


I20 


GENERAL  BIOLOGY 


layer  of  cells  that  is  protective  to  the  moist  internal  tissues. 

This  surface  layer  is  epidermis.     Examined  with  a  lens,  it 

will  be  seen  to  be  marked  out  in  minute  polygonal  areas  all 

over  the  upper  surface 
of  the  thallus  and  on 
close  inspection  a  minute 
pore  will  be  seen  in  the 
middle  of  each  of  these 
areas. 

An  examination  of  a 
cross  section  of  the  thal- 
lus, fig.  70  a,  b,  shows 
clearly  the  relation  of 
parts.  The  thallus  is  a 
large  aggregate  of  cells, 
and  the  cells  are  highly 
differentiated .  They 
form  two  principal  kinds 
of  tissue: — 

Epidermis,  of  flat 
transparent  cells  that 
cover  the  whole  exterior, 
some  of  which  are  modi- 
fied slightly  in  shape  to 
form  the  borders  of  the 
breathing  pores,  and 
others  are  inodified  very 
greatly,  being  extended 

into    long   filaments,    to  form    the    rhizoids    (fig.   70  b,  e). 
Parenchyma,  of  softer  cells,  richer  in  protoplasm,  filling 

the  whole  interior   and    differentiated  into    two    principal 

sorts  (fig.  70  (i,  w  and  v) — : 

I.     Assimilatory  parenchyma  of  smaller,  thin  walled  cells, 

containing  abundant   chlorophyl,  and  situated  in  an  upper 


e  ^ 


=4 


Fig.  70.  Conocephalus.  a,  cross  section  of 
the  thallus,  showing  rhizoids  and  scales 
beneath;  6,  a  bit  of  the  same  more  en- 
larged; p,  breathing  pore  in  the  upper 
epidermis;  r,  rhizoids;  s,  scale;  t,  one  of 
the  areas  about  a  pore  (empty) ;  v,  common 
parenchyma;  c,  a  breathing  pore,  as  seen 
from  the  surface;  d,  details  of  a  single 
area;  /?,  pore;  m,  assimilatory  parenchyma; 
V,  common  parenchyma,  e,  a  single  entire 
rhizoid  cell. 


ORGANIC  EVOLUTION  121 

stratum,  where  they  are  in  communication  with  the  air 
through  the  pores,  and  with  sunlight,  which  pene- 
trates the  transparent  epidermis.  These  differ  among 
themselves  in  form  according  to  their  situation. 

2.  Common  parenchyma,  of  bulky,  colorless  cells  com- 
posing the  thicker  interior  stratum,  which  gives  form  to  the 
thallus.  A  few  common  parenchyma  cells  rise  above  the  gen- 
eral level,  passing  between  groups  of  assimilatory  cells  to 
mark  out  the  areas  already  seen  from  the  surface. 

These  are  the  primary  tissues  of  all  the  higher  plants. 

Such  integration  of  cells  into  a  unit  organism  of  mutually 
dependent  parts,  we  have  not  found  before.  Inthealgaswe 
have  studied,  the  cells  are  more  loosely  associated  together, 
less  differentiated,  and  physiologically  more  independent. 
When  every  cell  is  in  contact  with  the  water  that  contains 
its  food,  there  is  no  need  of  special  feeding  organs. 

But  with  the  assumption  of  terrestrial  life,  the  sort  of 
division  of  labor  that  we  have  just  been  considering  has 
taken  place  among  the  cells  of  the  liverwort.  Different 
plant  functions  are  assumed  by  different  groups  of 
cells;  that  of  getting  carbon  from  the  air  by  the  cells  of 
the  assimilatory  parenchyma ;  that  of  getting  the  mineral 
matters  from  the  soil,  mainly  by  the  rhizoid  cells;  that  of 
protecting  the  protoplasm  from  the  new  peril  of  evaporation, 
by  the  cells  of  the  epidermis,  etc.;  each  group  doubtless 
improving  in  capacity  for  its  special  work,  as  it  is  relieved 
of  the  work  now  performed  by  other  cell  groups. 

Cell  division  is  localized  in  the  liverworts,  and  in  all  the 
higher  plants.  It  occurs  in  Conocephalus  only  at  growing 
points  located  in  the  notched  tips  of  the  stem  and  branches. 
There  new  cells  are  formed  during  the  growing  season. 
They  are  at  first  minute  and  rich  in  protoplasm.  They 
rapidly  increase  in  size  and  differentiate  into  the  kinds  of 
tissue  just  described,  and  take  their  places,  to  remain  of  one 
form  until  the  death  of  the  stem. 


122 


GENERAL   BIOLOGT 


Reproductive  cells  are  pro- 
duced by  another  kind  of 
differentiation  from  the  grow- 
ing points.  On  some  of  the 
branches,  sperm  cells  and  egg 
cells  are  developed  in  special 
receptacles  (gonangia),  the 
former  in  groups,  the  latter, 
singly.  The  container  for  the 
sperms  is  called  (as  in  plants 
generally)  the  antheridimn.^^ 
A  number  of  antheridia  are 
immersed  together  in  the  top 
of  a  disc-shaped  receptacle,  (the 
^       ^,    „  ,   ,  ,       antheridial  disc    or    antheridio- 

riG.     71.    Conocepnalus.    a,  anthe- 
ridial   disc,  showing    antheridia     phore,    fig:.     7 1     a,    b) .       The    COn- 
m  vertical  section;  b,  the  same     x-  '        o       # 

c,  archegonio-    taincr  for  the  egg  is  called  an 


in  surface   view; 
phore,    showing    archegonia    in 
vertical  section;  d,  the  same  in     Ql'cJie P'OHiumA 
surface     view;     e,    the    mature  ° 

archegonial  disc,  bearing  sporo- 
phytes  (one  opened  and  shed- 
ding the  spores) . 


Archegonia  are  developed  upon 
a  receptacle  {archegonio phore)  of 


a  nature  similar  to,  but  of  a  form  very 
different  from  that  which  bears  the  an- 
theridia. It  is  a  conic-capped,  mushroom- 
shaped  organ  (fig.  71  c,d).  The  arche- 
gonia are  inserted  underneath  the  cap^ 
Each  archegonium  (fig.  72  .4) ,  is  a  hollow 
flask-shaped  organ;  the  swollen  base  0£ 
the  flask  (w^hich  contains  the  single  egg    Fig.  72.  Conocephaius, 

A,   archegonium  in  ver- 
Cell)      is      inserted  upon    the      tissues     of     tical  section;  e-,  egg  cell; 

r      1         n       1       ^^'  ^^^  sporophvte;    /, 
the  disc,  and   the  open  neck    of   the    flask     foot;     g,   stalk;    /j,  spo- 
rangium; C,  contents  of 
is   directed   downward.  sporangium;    j,  spores; 

k   elaters. 

*This  is  the  equivalent  of  the  better  term  spermary,  which  we 
have  used  hitherto.  It  is  in  almost  universal  use  in  botanical  text 
books. 

fA  special  botanical  term  for  one  type  of  ovary. 


ORGANIC   EVOLUTION  123 

During  the  fall  and  winter  the  disc  is  low  and  inconspicu- 
ous, being  contained  in  a  circular  pit  in  the  top  of  the  thal- 
lus,  with  only  the  conic  cap  projecting.  It  is  surrounded  by 
a  circular  cleft  which  admits  of  access  to  the  archegonia 
when  these  are  mature.  The  sperms  are  free  swimming 
cells  of  strictly  aquatic  habit.  They  can  make  their  egress 
from  the  antheridia  and  swim  about  to  find  the  egg  cells 
only  when  rain  or  dew  has  supplied  sufficient  water  for  the 
purpose. 

In  early  spring  the  stalk  of  the  archegonial  disc  elongates 
enormously  and  pushes  the  cap  up  in  the  air  to  a  height  of 
two  or  three  inches  (fig.  71  ^).  This  lengthening  is  not 
brought  about  by  the  production  of  new  cells,  but  by  the 
further  development  of  those  already  present.  In  the  cen- 
ter of  the  transparent  stalk  may  be  seen  an  axial  bundle  of 
cells  that  have  become  extraordinarily  lengthened,  and 
that  form  when  fully  developed  and  hollow,  a  bundle  of 
capillary  tubes,  which  facilitate  the  transport  of  food 
materials  from  the  thallus  below  to  the  maturing  spores 
above.  These  capillary  cells  are  the  most  specialized  cells 
in  the  body  of  the  liverwort. 

Development. — From  the  fertilized  egg  cell  there  devel- 
ops, not  another  thallus  like  the  one  that  produced  it,  but  a 
plant  body  of  a  very  different  sort,  (fig.  72  M),  called  a 
sporophyte  (or  sporogonium) .  This  develops  as  follows: 
The  egg  cell  divides  repeatedly,  forming  a  mass  of  cells  that 
distends  the  walls  of  the  archegonium.  This  cell  mass  then 
differentiates  gradually  into  the  three  parts  of  the  sporo- 
phyte, foot,  stalk  and  sporangium.  The  sporophyte 
develops  at  the  expense  of  the  archegoniophore ;  its  foot 
remains  immersed  in  the  tissues  surrounding  the  base  of  the 
archegonium,  and  serves  as  the  food-absorbing  organ.  The 
stalk  gradually  elongates  and  pushes  the  sporangium  down- 
ward toward  the  outer  world.     The  sporangium  develops  a 


124  GENERAL  BIOLOGY 

protective  outer  wall,  and  the  cell  mass  contained  in  it 
finally  develops  into  a  very  great  number  of  minute  round- 
ish reproductive  cells  called  spores,  intermixed  with  sterile 
cells  called,  because  of  their  function,  elaters.  Upon  the 
drying  and  bursting  of  the  sporangium  wall,  the  elaters,  by 
their  twisting  and  turning,  assist  in  the  scattering  of  the 
spores. 

Alternation  of  generations. — From  those  spores  which, 
when  scattered  abroad,  find  suitable  lodgment  and  food  for 
growth,  there  develop  new  thalli,  like  the  one  with  which 
we  started.  Thus  there  are  two  distinct  parts  to  the  life 
cycle  of  Conocephalus ;  a  large  independently-feeding  green 
plant,  which,  because  it  produces  the  sex  cells  (gametes)  is 
called  the  gametophyte,  and  a  small,  dependent  sporophyte 
producing  the  spores.  The  former  is  a  sexual,  the  latter  an 
asexual  generation.  This  phenomenon  is  known  as  alter- 
nation of  generations.  Because  of  its  importance  in  the 
green    plant   series,  gametophyte  and-  sporophyte    should 

be  clearly  distinguished  at  once,  the 
former  producing  the  eggs  and 
sperms,  the  latter  producing  the 
spores ;  the  one  regularly  develop- 
ing from  the  reproductive  cells 
produced  by  the  other. 

Other    Bryophytes. — Riccia    (fig. 
Fir;.  73.    A  spray  of  the  liver-    7  s)  IS  a  simpler  Hvcrwort ,  that  has  the 
wort.  Riccia  flmtans.  archcgonia  and  antheridia  immersed 

in  the  upper  side  of  the  thallus.  J ungermannia  (fig.  74)  is  a 
liverwort  of  more  highly  specialized  form,  in  which  the  midrib 
of  the  thallus  has  become  the  plant  stem,  and  the  broad 
margins  have  become  differentiated  into  leaves.  These, 
however,  are  rather  crude  in  form  and  simple  in  structure, 
lacking  veins  and  even  a  mid  rib,  and  consisting  of  a 
single  layer  of  chlorophyll  bearing  cells.     But  they  indicate 


ORGANIC  EVOLUTION 


125 


relationship  with  the  simple  mosses.     The  leaves  of  mosses 
are  better    developed,    possessing    a  mid  rib,  and  usually  a 


Fig.  74.     Three  "leafy  liverworts"  Jungermannia.  three  species.     (Copiedfrom 
Gray's  Manual  of  Botany,  a  classical  manual  of   North  American  plants). 

margin  of  close  knit    cells,    and    are  often  borne  on  erect 

stems. 

A  comparison  of  the  sporophyte    phase    in    bryophytes 

will  be  most  instructive.  It 
is  in  this  group  we  first  find 
alternation  of  generations 
fully  established  with  an 
organized  sporophyte.  While 
there  is  reproduction  by 
means  of  both  sex  cells  and 
spores  among  the  thallophy- 
tes,  there  is  rarely  the  regular 
alternation  between  them  and 
never  such  differentiation  of 
a  distinct  sporophyte  phase  as 
we  find  there.  This  phase 
finds  a  simple  expression  in 
Riccia.  From  the  egg  there  de- 
velops a  single  spherical  shell 
of  (ephemeral)  sterile  cells 
containing  spores      (Fig.    75) 


Fig.  75.  Section  of  the  simple  sporo- 
phyte of  Riccia  naians,  inclosed  with- 
in the  distended  wall  of  the  archego- 
nium).  Note  that  all  the  cells  of  the 
sporophyte  are  spores  save  a  single 
peripheral  layer  that  is  dotted  in  the 
figure  (after  Chamberlain). 


126 


GENERAL   BIOLOGY 


only.     No  foot  nor  stalk  appear ;     only   sporangium :  and 
in  the  sporangium,  no  sterile  cells;  only  spores. 

The  maximum  development  of  sporophyte  phase  in  the 
bryophyte  group  of  plants  is  found  in  the  mosses,  in  which 
the  archegonia  are  terminal  upQn  a  stem  or  branch,  and, 

although  produced  in  clus- 
ters,but  a  single  egg  normally 
develops  to  maturity.  From 
the  fertilized  egg  there  de- 
velops a  sporophyte  of  great 
length  which  early  ruptures 
the  archegonium  wall,  carry- 
ing the  upper  end  of  it  up 
into  view  as  the  calyptra. 
This  falls  away  at  maturity. 
Foot,  stalk  and  sporangium 
are  highly  differentiated. 
The  foot  is  buried  in  the  tis- 
sues of  the  parent  gameto- 
phyte,  whence  it  draws 
nourishment  for  develop- 
ment, as  in  the  liverworts. 
The  stalk  is  long  and  pushes 
the  sporangium  up  conspicu- 
ously into  vicAv.  The  spo- 
rangium is  composed  of  a 
number  of  highly  diiferentia- 
ted  sterile  parts.  It  contains 
no  elaters,  and  the  spores 
are  situate  in  a  cylindric  layer  surrounding  a  central  core 
of  parenchyma  cells  (called  the  columella),  and  usually  cover- 
ed over  by  a  detachable  cap,  the  operculum,  that  grows  be- 
neath the  calyptra  and  is  a  part  of  the  sporangium  itself. 
Underneath    the   operculum    there    is   often    a   peripheral 


Fig.  76.  The  moss  sporophyte.  A,C,  F, 
successive  stages  in  its  development; 
c,  calyptra  (detached  top  of  archego- 
nium; X,  foot;  y,  stalk;  z,  sporan- 
gium; M,  longitudinal  section  of  the 
sporangium ;  o,  operculum  (detached) ; 
/,  columella;  r,  respiratory  paren- 
chyma; 5,  spores;  r,  teeth;  j^,  breath- 
ing pore  (stomate),  and  the  same 
below  in  surface  view. 


ORGANIC   EVOLUTION  127 

row  of  teeth  attached  at  the  margin,  with  free  tips  that 
meet  at  the  center  of  the  columella.  These  regulate  the 
dispersal  of  the  spores,  by  lifting  (as  if  by  hinges  at  their 
bases)  when  dry,  and  exposing  the  top  of  the  spore  cavity, 
allowing  the  spores  to  be  shaken  or  to  fall  out,  and  closing 
down  by  hygroscopic  movement  when  wet. 

Perhaps  the  most  significant  feature  is  the  appearance  of 
a  loose  layer  of  chlorophyl  bearing  parenchyma  in  the  outer 
wall  of  the  sporangium,  and  the  development  in  the  epider- 
mis covering  the  base  of  it,  of  a  few  breathing  pores  (sto- 
mates)  of  a  new  type.  This  type  is  the  prevailing  one 
in  the  following  groups  of  plants.  Thus  the  sporophyte  is 
able  to  gather  some  carbon  for  itself,  though  dependent  on 
the  gametophyte  for  other  elements  of  its  food. 

We  have  already  seen  that,  as  compared  with  the  algae, 
the  bryophytes  have  attained  to  a  higher  grade  of  bodily 
structure,  and  have  acquired  an  organization  that  is 
directly  related  to  terrestrial  life.  The  new  features  of  their 
life  history,  also,  are  related  to  this  changed  environment. 
They  brought  with  them  from  the  water  and  have  one  and 
all  retained  a  strictly  aquatic  mode  of  fertilization.  All 
have  free-swimming  sperm  cells:  and  the  distance  between 
the  antheridia  and  the  archegonia  must  be  covered  by  water 
at  the  time  the  sex  cells  ripen,  else  fertilization  cannot  take 
place.  But  spores  do  not  require  to  be  fertilized:  and  the 
introduction  of  the  spore-producing  generation  seems  to 
have  been  the  means  availed  of  for  securing  the  production 
and  distribution  of  a  host  of  new  individuals  while  avoiding 
the  exigencies  of  fertilization  under  the  changed  conditions. 

Study    I'/.      An  examination  of  hryophyte  characters. 

Materials  needed:  Fresh  green  specimens  of  Conocepha- 
lus  or  other  thalloid  liverwort;  either  fresh  or  preserved 
specimens  bearing  antheridia  and  archegonia,  older  speci- 
mens bearing  sporophytes;     also,  sets  of  prepared  slides. 


128  GENERAL   BIOLOGY 

The  student  should  study:  i)  in  the  fresh  thallus,  its 
form  and  mode  of  branching,  the  location  of  its  growing 
points,  its  exposure  to  light.  2)  The  areas  about  the  pores 
of  the  upper  surface  (the  details  of  the  latter  will  easily  be 
made  out  in  thin  tangential  sections  cut  freehand  with  a 
razor  from  the  upper  surface). 

3)  The  scales  and  rhizoids  of  the  lower  surface  and  the 
attachment  to  the  soil. 

4)  The  details  of  structure  of  archegoniophore  and  anthe- 
ridiophore.  Study  vertical  sections  of  these,  if  such  be  at 
hand. 

5)  The  details  of  structure  in  cross  sections  of  the  thallus 
(possible  in  freehand  sections  from  fresh  tissues,  but  pre- 
pared sections  will  be  much  better,  if  well  prepared) . 

6)  The  excessively  elongate  cells  of  the  axial  bundle  of 
the  stalk  of  the  mature  (easily  withdrawn  with  forceps 
from  the  stalks  preserved  in  formalin,  and  should  be 
mounted  outspread  in  a  drop  of  water  or  formalin  solution) . 
Compare  these  in  form  with  those  of  the  outer  wall  of  the 
stalk. 

7)  The  mature  sporophyte  (easily  dissected  out  with 
needles  under  a  lens) .  Study  also  its  development  from  the 
egg,  if  slides  are  available  for  this. 

8)  The  form  and  structure  of  the  spores  and  of  the  elaters. 

The  record  of  the  work  done  may  consist  of  notes  on  and 
drawings  of  the  more  important  structures  studied. 

9)  The  structure  of  the  moss  sporangium  (ep.sily  made  out 
in  longitudinal  sections:  freehand  sections  will  do  for  this, 
if  permanent  slides  are  not  available)  identifying  the  parts 
mentioned  in  the  explanation  to  figure  76. 

PTERIDOPHYTES.       FERNS,  ETC. 

This  is  a  group  of  plants  of  larger  size  than  bryophytes 
and  of  still  greater  diversity  of  appearance.     It  differs  most 


ORGANIC   EVOLUTION 


129 


remarkably  in  the   size  and  predominance  to  which  the 
sporophyte  has  attained. 

The  fern  (Pteris) . — The  gametophyte  of  the  fern  will  serve 
well  to  connect  with  preceding  studies.     It  is  a  little  heart- 
shaped  thallus  (called  the  pro- 
thallium),    hardly   exceeding  a 
quarter  of  an  inch  in  diameter 
when  grown.     Its  structure  is 
even  more  simple  than  that  of 
the     thallus     of    a     liverwort. 
There     is    the     same     copious 
development  of  rhizoids,   con- 
necting  it   with   the   soil,    but 
there  is  less  differentiation  of 
the  tissues  of  the  thallus  itself, 
there  being  no  sharp  distinction 
of  special   assimilatory  paren- 
chyma    and    no     pores.     The 
growing  point  is  in  the  notched 
tip,  protected  as  before  by  the 
lobes  extended  at  either  side  of 
it.     The  archegonia  and  anthe- 
ridia    are    developed    on    the 
under  side  of  the  thallus,  and 
open  downward;     the   former  are   arranged   in   a   cluster, 
nearer  the  growing  point  (fig.  77).     The  sperms  are  motile 
and  swim  about  when  mature,  if  favoring  rain  or  dew  give 
them  opportunity.     Many  of  them  mature  in  advance  of 
the  maturing  of  the  eggs  of  the  same  thallus,  thus  favoring 
cross-fertilization. 

Thus,  it  will  be  seen  there  is  quite  a  general  similarity 
between  the  prothallium  of  the  fern  and  the  thallus  of  a 
simple   liverwort.       But  this  phase  of   the   fern  is   least 


Fig.  77.  The  fern,  a,  the  gameto- 
phyte phase,  inverted  and  seen 
from  lower  surface;  5,  the  spore 
from  which  it  grew;  r,  rhizoids; 
p,  the  growing  point  in  the  bottom 
of  the  apical  notch;  o,  archegonia 
and  t,  antheridia;  b,a.  single  arche- 
gonium  in  vertical  section;  e,  egg 
cell;  c,  a  single  antheridium,  with 
developing  sperm  cells ;  d,  a  single 
[mature  sperm  cell. 


I30 


GENERAL   BIOLOGY 


developed,  and  the  sporophyte  phase  is,  save   in  its  origin, 


Fig.  78.  Fern  embryos,  a,  after  the  first  division  into  two  cells; 
b,  an  embryo  showing  the  begmnings  of  root  (r),  stem  (5)  and 
leaf  (/);  c,  an  older  embryo,  the  leaf  tip  turning  upward,  vas- 
cular bundles  {v),  developing;   /,  foot. 

exceedingly  different.     The  comparison  of  sporophytes  will, 

therefore,  be  more  readily  made  if  it 
be  a  comparison  of  early  stages. 

The  sporophyte. — The  fertilized  egg 
divides  (fig.  78  a)  and  produces  a 
mass  of  cells  within  the  walls  of  the 
archegonium.  From  this  cell  mass 
there  are  early  differentiated  a  num- 
ber of  parts,  one  of  which  clearly  cor- 
responds to  the  foot  of  such  sporo- 
phytes as  we  have  seen  hitherto,  it 
being  a  food  absorbing  organ  im- 
mersed in  the  tissues  of  the  parent 
gametophyte  (fig.  ySf).  From  the 
remainder  (which  corresponds  only  in 
a  general  way  to  the  sLalk)  root  and 
leaf  develop,  the  root  extending  down- 
ward into  the  soil,  branching  and 
developing  rhizoids  for  independent 
foraging  there,  the  leaf  passing  out 
between  the  lobes  at  the  apex  of  the  thallus  and  turning  up- 
ward to  the  light  and  expanding,  taking  tip  its  proper 
work  of    carbon  dioxide  reduction     (fig.     79).      Thus    the 


Fig.  79.  The  fern  sporo- 
phyte, in  the  first  leaf, 
but  still  attached  to  the 
parent  gametophyte. 


ORGANIC  EVOLUTION 


131 


:  porophyte  early  acquires  a  complete  set 
of  foraging  organs  and  becomes  indepen- 
dent of  the  parent  gametophyte.  The  body 
of  the  embryo  grows  out  more  slowly  into 
the  underground  horizontal  stem  (rhizome) 
of  the  fern,  producing  as  it  grows  new 
leaves  that  rise  to  the  light,  and  for  a  time 
increase  in  size  and  complexity,  and  new 
and  larger  roots  that  spread  through  the 
soil.  So,  the  sporophyte  is  launched  upon 
its  career  of  independent  existence;  and 
not  being  limited  to  the  supply  of  food 
that  a  small  parent  thallus  can  furnish,  spore 
production  is  long  delayed.  A  long  growth 
Fig.  80.    Diagram  ii-   period     intervenes.       A 

lustrating  the  intake     ,  .,  ,        ^        . 

of  food  materials  at     large  plant  body  IS    pro- 
root  and  leaf  in  the      .,  .,  1   •    1 

auced,  which  when 
mature  develops  spor- 
angia in  extraordinary 
numbers   upon  the  sur- 


fern,  and  the  trans- 
portation system  of 
vascular  bundles 
connecting  the  two 
sources  of  supply 
with  all  parts  of  the 
plant  body. 

^     face  of  its  leaves. 


In  this  plant  body  the  food  absorbing 
organs  are  those  w4th  which  we  have  al- 
ready become  acquainted  in  the  bryophytes. 
The  rhizoids  surround  the  tips  of  the  root- 
lets in  the  soil  (fig.  80).  The  assimilatory 
parenchyma  is  chiefly  located  in  the  leaves, 
protected  by  a  layer  of  transparent  epider- 
mis, composed  of  thin  flat,  curiously  inter- 
locking cells  (fig.  81).  The  oxygen  of  the 
air  finds  ingress  through  pores  (stomates)  of  the  sort 
already  seen  in  the  moss  sporophyte  (fig.  76  M,  p). 

The  development  of  a  plant  body  of  so  greatly  increased 
size  is  made  possible  by  the  development  of  new  structures 
out  of  the  parenchyma.     These  are  of  two  sorts: — 


132 


GENERAL    BIOLOGY 


Supporting  tissues,   necessitated    by  increasing  size  and 
^^  weight. 

Conducting  tissues,  necessitated  by 
the  increased  distance  between  the  two 
sources  of  intake  of  food  materials,  the 
rhizoids  deep  in  the  soil,  and  the  assimi- 
latory  parenchyma  of  the  leaf,  lifted 
high  in  the  air. 

The  position  of  these  new  parts  in 
the  plant  body  can  best  be  learned  by 
an  examination  of  the  structure  of  the 
mature  stem  in  a  cross  section  of 
which  (fig.  82)  they  may  be  seen  with 
the  unaided  eye.  As  before,  the  sur- 
face layer  of  cells  is  epidermis,  and  the 
whole  of  the  soft  part  of  the  interior  is 
parenchyma.  The  new  tissues  whose 
function  is  chiefly  or  wholly  supportive 
are  more  or  less  brownish  in  color  and 
arranged  i)  in  a  peripheral  layer  just 
beneath  the  epidermis,  and  2)  in  two  or 
more  broad,  darker  colored  strands  of 
tissue  extending  through  the  midst  of 
the  parenchyma.  These  tissues  consist 
of  thickened  and  closely  united  walls  of 
empty  cells.  The  inner  darker  strands 
may  readily  be  traced  through  the  soft 
parenchyma,  and  followed  where  they  branch  out  into  the 
bases  of  roots  and  leaves. 

The  tissues  whose  most  important  function  is  the  conduc- 
tion of  food  materials  (though  certain  of  their  elements 
also  serve  for  support)  are  found  in  the  vascular  bundles, 
which,  also  are  readily  seen  in  cross  section  of  the  stem. 
They  are  of  various  sizes,  and  not  constant  in  number,  but 


Fig.  81.  Leaf  epidermis 
of  the  fern ;  5^  stomates 
or  leaf  pores. 


ORGANIC  EVOLUTION 


133 


are  easily  recognizable  by  the  finely  perforate  appearance 
that  the  cut  end  of  each  bundle  presents.  These  bundles, 
like  the  internal  strands  of  supporting  tissue,  may  be  traced 
through  the  soft  parenchyma  by  dissection,  and  followed 
at  their  branchings  out  into  the  base  of  roots  and  leaves. 

Vascular  Bundles. — These  bundles  constitute  the  trans- 
portation system  of  the  sporophyte,  condition  its  growth, 
enable  it  to  take  possession  of  larger  areas  and  deeper  layers 

of  soil,  to  rise  higher  and  to 
spread  out  more  widely  in  the 
air  and  light ,  and  are  therefore , 
structures  of  first  importance 
in  the  fern.  They  are  com- 
pound structures  formed  out  of 
the  common  undifferentiated 
tissue  (called  the  meristem) 
by  the  ordinary  processes  of 
cell  growth  and  differentia- 
tion. They  are  made  up  of  a 
variety  of  tissues  serving  vari- 
ous purposes.  The  most  im- 
portant conducting  tissues  are  two:  i)tracheids,  the  tubes  of 
the  largest  diameter  which  give  the  perforate  appearance  to 
the  cross  section  of  the  bundle;  these  are  the  lignified 
walls  of  elongated  and  empty  cells,  and  serve  chiefly  for  the 
conduction  of  water,  with  whatever  may  be  dissolved  in  it. 
2)  sieve  tubes:  these  are  living,  greatly  elongated,  exten- 
sively vacuolated,  but  yet  protoplasmic  cells,  with  oblique 
overlapping  ends  whose  walls  exhibit  groups  of  fine 
perforations.  Through  the  latter  there  is  protoplasmic 
continuity  between  adjacent  cells.  Albuminoid  substances 
are  distributed  through  these  cells  by  diffusion  through  the 
continuous  protoplasm.  The  chief  supporting  tissues  of 
the  bundles  are  two:     i)  the  tracheids  already  mentioned, 


Fig.  82.  Diagram  of  a  cross  section 
of  the  underground  stem.{rhizonic) 
of  the  fern  (Pteris).  e,  epidermis; 
/,  vascular  bundle;  g,  inner  strands 
of  supporting  tissue  {sclerenchyina) ; 
h,  peripheral  layer  of  supporting 
tissue. 


134 


GENERAL   BIOLOGY 


and  2)  the  bast  fibres,  situated  nearer  the  periphery  of  the 
bundle.     The  remainder  of  the  bundle  is  parenchyma,  little 


Fig.  83.  Vascular  bundle  of  the  fern  (Pteris)  after  Sedgwick  and  Wil- 
son, a,  longitudinal  section;  b,  cross  section;  /  p,  common  paren- 
chyma; b  s,  bundle  sheath,  p  s.  phloem  sheath  of  parenchyma;  b  f, 
best  fibres;  5  t,  sieve  tubes;  p  p,  phloem  parenchyma;  t,  tracheids 
(wood  tub6s) ;  w  p,  wood  parenchyma;  5  v,  spiral  vessel. 

differentiated.     It   constitutes  the   packing,   so  to   speak. 


ORGANIC   EVOLUTION 


US 


between  the  other  more  speciaHzed  parts.     The  distribution 
of  these  tissues  in  the  bundles  is  indicated  in  figure  83. 

The  distribution  of  the  bundles 
themselves  is  such  that  every  con- 
siderable part  of  the  plant  body  is  put 
in  vascular  communication  with  every 
other  part.  The  differentiation  of 
vessels  follows  closely  every  growing 
point,  down  into  root  and  rootlet,  up 
into  leafstalk  and  blade  and  lobe, 
through  every  vein  and  veinlet.  Some 
branchlet  of  a  vessel  ends  not  far 
from  every  group  of  rhizoids  in  the  soil, 
not  far  away  from  every  stomate  in  the 
leaf.  The  venation  of  the  leaf  "(fig. 
163),  is  the  map  of  the  distribution 
of  the  vessels  therein. 

The  new  organs  of  the  fern  are  root 
and  leaf,  both  of  them,  mere  extensions 
of  the  plant  body,  carrying  out  into 
new  and  wider  foraging  ground  the 
original  foraging  organs,  rhizoids  and 
chlorophyl-bearing  cells.  The  moss 
has  no  better  circulatory  apparatus  than  a  simple  axial 
bundle  of  slightly  elongated  parenchyma  cells;  it  develops 
no  roots  and  can  forage  in  the  soil  only  the  length  of  its 
rhizoids.  Clearly,  the  structures  of  the  fern  we  have  just 
noted  sufficiently  account  for  the  larger  size  to  which  the 
Pteridophytes  have  attained. 

Spore  formation  is  greatly  delayed,  but  in  the  end  it  occurs 
on  a  much  larger  scale  by  reason  of  the  large  plant  body 
built  up  and  capable  of  nourishing  spores;  moreover,  it 
may  be  repeated  by  the  same  sporophyte  year  after  year. 
In  the  bracken     fern,  sporangia     (fig.  84)   are     developed 


Fig.  84.  Sporangfium  and 
spores  of  a  fern,  ^  ,  side 
view;  b,  rear  view;  n, 
the  annulus;  r,  its  front 
end,  which  lifts  on  dry- 
ing and  ruptures  the 
wall    below;  s.    a  spore 


136 


GENERAL  BIOLOGY 


under  the  rolled  margin  of  the  leaf,  in  small  clusters  (called 
sort).  Each  sporangium  is  borne  on  a  slender  pedicel;  its 
walls  are  composed  of  thin  epidermal  cells ;  one  line  of  these 
cells,  encircling  the  top  of  the  sporangium  is  differentiated 
into  a  ring  (the  annulus)  of  thick-walled  hygroscopic  cells, 
which  at  maturity  burst  the  capsule  by  their  elasticity, 
scattering  the  spores.  The  spores  which  fall  in  suitable  place 
germinate  after  the  manner  shown  in  (fig.  85),  and  grow 
into  thin,  flat  heart-shaped  prothallia. 


Fig.  85.  Development  of  the  fern  gametophyte  from  the 
spore;  figs.  1  to  6  show  successive  stages;  figs.  3  and  4 
show  the  establishment  of  an  apical  cell  and  growing 
point;  fig.  6  shows  the  second  rhizoid. 

Comparing  fern  and  liverwort,  we  see  great  similarity  in 
reproductive  organs  and  methods,  considerable  similarity  in 
the  gametophyte  phase,  and  great  divergence  in  form,  size, 
structure  and  manner  of  life  of  the  sporophyte. 

Other  pteridophytes. — The  common  horsetail  (Equisetum) 
will  serve  to  illustrate  the  kind  of  differences  presented  by 
another  group  of  pteridophytes.  The  sporophyte  phase  of 
the  horsetail  is  leafless,  but  bears  green  naked  branches 
which  arise  from  an  underground  rhizome.     The  chlorophyl 


ORGANIC  EVOLUTION 


137 


bearing  parenchyma  is  located  in  the  furrows  of  the 
branches.  The  furrows  extend  up  and  down,  and  the 
chlorophyll  bearing  cells  communicate  with  the  air  by  pores 
or  stomates  arranged  in  two  rows  in  each  furrow.  The  sup- 
porting tissues,  (aside  from  the 
unusualy  stiff  epidermis),  are 
located  in  the  ridges,  which 
they  chiefly  compose.  The 
branches  are  hollow,  and  the 
vascular  bundles  are  arranged 
radially  around  the  main  cen- 
tral cavity,  opposite  the  ridges 
upon  the  surface.  Each 
branch  is  divided  into  seg- 
ments by  a  scries  of  nodes  (at 
which  it  breaks  when  pulled, 
whence  the  popular  name, 
"joint-grass").  The  arrange- 
ment of  ridges  and  valleys, 
of  vascular  bundles  and  cavi- 
ties, of  green  respiratory  par- 
enchyma in  the  valleys  and 
the  broad  bands  of  support- 
ing tissue  in  the  ridges,  are 
readily  seen  in  cross  sections 
of  fresh  stems.  The  epidermis 
is  covered  with  secreted  nod- 
ules of  silica  which  render  the 
branches  rough  to  the  touch 
(whence  the  popular  name 
"scouring-rush") . 

The  spores  are    developed 
in  numerous  sporangia    that 
grow   underneath  the  scales  of  a  fruiting  cone  (fig.  86  a,  b,  c) 


Fig.  86.  The  common  equisetum  {E. 
arvense).  a,  a  fruiting  spray;  b 
and  c,  two  scales  from  the  fruiting 
cone,  showing  marginal  sporangia; 
d,  two  spores,  with  their  hydro- 
scopic elaters  partly  unrolled;  e,  a 
bit  of  underground  stem,  bearing  a 
round  tuber. 


138 


GENERAL  BIOLOGY 


at  the    top    of  the  stem,  as  indicated.     The  outer     cover- 

ing  of  each  spore  is  spHt  into  four  long 
involute  strips,  which  serve  as  elaters, 
and,  being  exceedingly  hydroscopic, 
these  extend  and  roll  up  again  with  slight 
changes  of  moisture  and  push  the  spores 
out  of  the  sporangia. 

Two  kinds  of  Gametophytes. — AVhile 
the  spores  all  look  alike,  some  of  them 
on  germination  develop  into  small  pro- 
thallia  which  produce  only  antheridia 
and  others  grow  into  larger  prothallia 
which  produce  the  archegonia. 

The  prothallia  (fig.  87)  are  therefore 
unisexual,  as  in  some  of  the  mosses,  but 
each  thallus  and  especially  the  male,  is 
of  very  small  size.  Fertilization  occurs 
with  the  aid  of  water  for  transport  of 
the  sperms  as  in  the  fern,  and  the  devel- 
opment of  the  sporophyte  from  the 
fertilized  egg  follows  the  same  general 
course. 

Selaginella  (fig.  S8,)  is  another  pteridophyte  with  a  trailing 
stem  bearing  small  two-ranked  leaves  and  lesser  scales.  It 
is  especially  interesting  on  account  of  the  development  of  its 
spores.  The  sporangia  are  located  in  the  axils  of  scales 
aggregated  in  several  terminal  laterally  flattened  spikes 
and  are  of  two  sorts  large  (macrosporangia) ,  and  small 
(microsporangia) .  The  spores  within  them  are  of  two 
sorts,  large  ones  (macrospores) ,  four  in  number  developed 
in  the  macrosporangia,  and  small  ones  (microspores) 
developed  in  large  numbers  in  the  microsporangia.  It  is 
less  surprising,  therefore,  that  there  should  develop  from 
them  two  sorts  of  prothallia ;     but  the  prothallia  themselves 


Fig.  87.  Male  and 
female  prothallia  of 
equisetum  (after 
Goebel).  a,  the 
male  prothallium, 
with  marginal  an- 
theridia; 6,  a  sperm 
cell;  c,  the  female 
prothallium  bearing 
three  archegonia. 


ORGANIC  EVOLUTION 


139 


are  very  different  from  those  we  have  studied  hitherto. 
The  microspore  develops,  beginning  while  still  within  the 
microsporangium,  into  a  male  prothallium  of  microscopic 
size.  It  consists  when  mature  of  but  few  cells,  one  of  these 
representing  the  body  of  the  prothallium  and  the  others 
the  antheridial  wall,   inclosing   a    considerable    number  of 


Fig.  88.  Selaginella.  a  and  b,  tip  and  base  of  a  fruiting  spray;  c,  diagram 
of  a  fruiting  spike,  showing  macro  and  micro-sporangia  in  the  axils  of 
scales;  tf,  microsporangium  ;  e,  macrosporangium ; /,  the  male  prothal- 
lium, spore  mother  cells  dotted;  g,  as  single  sperm  cell,  h,  the  fe- 
male prothallium,  rupturing  the  wall  (w)  of  the  macrospore;  m,  a  new 
sporophyte  embryo ;  n,  its  suspensor,  and  p  its  growing  point ;  o,  the 
remains  of  an  old  archegonium;  r,  rhizoids. 

Sperm  cells.  There  are  no  rhizoids  or  other  nutritive 
organs  developed,  and  the  prothallium  is  short  lived  After 
a  few  cell  divisions  it  differentiates  the  sperm  cells,  which  are 
liberated  in  the  water  by  the  dissolution  of  the  surround- 
ing cells. 


140  GENERAL  BIOLOGY 

The  macrospore  likewise  begins  its  development  while  in 
the  sporangium.  It  contains,  however,  within  its  own  wall  a 
store  of  food  material,  upon  which  considerable  develop- 
ment is  possible.  The  spore  divides  repeatedly,  and  grow- 
ing at  the  expense  of  the  stored  food,  bursts  the  spore  wall, 
and  protrudes  as  a  small  prothallium  which  develops  a  few 
rudimentary  rhizoids,  and  later  a  few  archegonia  containing 
egg  cells.  These  are  developed  and  often  fertilized  before 
the  growth  of  the  prothallium  is  complete.  Since  the 
microspores  are  developed  in  the  upper  part  of  the  fruiting 
cones  they  may  fall  down  into  the  lower  scales. 

The  fertilized  egg  develops  foot,  stem,  root  and  leaf  as 
before,  and  in  addition  a  special  embryonic  organ  the  so- 
called  suspensop,  whose  function  it  is  to  keep  the  embryo 
pushed  down  against  the  prothallial  tissue  from  which  it 
must  obtain  its  food.  By  the  time  this  supply  is  exhausted 
the  embryo  has  developed  a  root,  bearing  rhizoids,  and  one 
or  two  pairs  of  minute  leaves  at  the  apex  of  the  stem,  and  is 
ready  to  get  food  for  itself  independently. 

The  predominance  of  the  sporophyte  phase  is  in  this 
plant,  very  marked.  The  gametophyte  is  here  not  only 
reduced  in  size,  but  wholly  dependent  on  the  antecedent 
sporophyte  for  food — the  reversal  of  the  conditions  with 
which  we  started. 

Study  i8.     Fern  development. 

Materials  needed:  Fronds,  bearing  ripe  and  immature 
sporangia ;  prothallia  in  all  stages  of  development  and  old 
ones  bearing  sporophytes. 

Study  the  grouping  of  the  sporangia  in  relation  to  each 
other  and  to  the  veins  of  the  leaf,  and  their  protective 
covering. 

Study  the  structure  of  the  mature  and  of  the  ruptured 
sporangia. 


ORGANIC  EVOLUTION  141 

Study  the  spores,  and,  if  material  be  at  hand,  their 
germination  also. 

Study  the  prothallia:  their  form,  their  parts,  their  arche- 
gonia  and  antheridia. 

Study  the  young  sporoph3rte,  both  before  and  after  the 
acquisition  of  independent  foraging  organs.  If  a  few  pre- 
pared sections  of  its  earlier  stages  of  development  are  at 
hand  they  will  be  especially  instructive. 

The  record  of  this  study  may  well  consist  in  a  brief 
account  of  the  life  history  of  the  fern,  with  drawings  and 
diagrams  to  illustrate  it. 

Study  ig.     The  general  structure  of  the  fern  sporophyte. 

Materials  needed:  A  growing  fern  plant;  fresh  or 
alcoholic  rhizomes  of  Pteris,  and  also  macerated  specimens 
of  same  for  use  in  tracing  vessels;  prepared  slides  of  leaf 
and  root  tips ;  mounted  sections  and  dissociation  prepara- 
tions of  vascular  bundle  elements. 

Study  the  distribution  of  the  vascular  system. 

Study  the  leaf:  The  epidermis  in  a  freshly  stripped  piece, 
mounted  in  alcohol;  the  air  spaces,  internal  tissues  and 
distribution  of  vessels  in  cross  sections. 

Study  the  root  tips,  the  arrangement  of  rhizoids,  the  loca- 
tion of  root  cap  and  vascular  bundles. 

Study  the  vascular  bundle  structure,  sufficiently  at  least 
to  locate  and  identify  the  principal  supporting  and  conduc- 
ting'tissue  elements. 

The  record  of  this  study  may  consist  in  notes  and  draw- 
ings of  things  observed. 

Study  20.     A    comparison    of   developmental    features     of 

other  pteridophytes. 

Materials  needed:  Fresh  stems  of  the  scouring  rush 
(Equisetum  hyemale) ;  fresh  fruiting  cones  of  the  common 
horsetail  (E.  arvense)  these  may  be  had  in  fine  condition  if 


142  GENERAL   BIOLOGY 

dug  up  in  winter  and  placed  under  a  bell  jar  a  week  in 
advance  of  need) :  fruiting  spikes  of  Selaginella,  and  also  if 
possible,  preserved  specimens  illustrating  the  development 
of  the  male  and  female  gametophytes. 

Study  the  Equisetum  stems  in  sections  (which  may  be 
cut  with  a  sharp  knife,  though  very  damaging  to  its  edge), 
locating  the  chief  structural  features  mentioned  in  preceding 
pages.  Especially  note  the  distribution  of  the  respiratory 
parenchyma  (of  bright  green  color  in  fresh  specimens)  and 
the  breathing  pores  leading  thereto;  these  latter  will  be 
better  seen  if  the  epidermis  be  stripped  from  one  of  the 
"valleys,"  mounted  flat,  and  studied. 

Study  the  fruiting  spike  of  equisetum,  its  constituent 
scales,  the  sporangia  these  bear,  and  the  spores.  Mount 
some  spores  uncovered  to  watch  through  the  microscope 
their  hygroscopic  activity ;  they  will  respond  instantly  to 
the  moisture  of  the  breath,  let  fall  upon  them  while  under 
observation. 

Stud}^  the  fruiting  spikes  and  the  macrospores  and  micro- 
spores of  Selaginella,  and  if  there  be  material  so  available, 
study  also  the  male  and  female  gametophytes  that  develop 
from  these  spores. 

The  record  of  this  study  may  consist  in  notes  and  draw- 
ings of  the  things  observed. 

SPERMATOPHYTES,    SEED    PLANTS,    OR    FLOWERING    PLANTS. 

These  are  the  dominant  land  plants  of  our  own  time. 
Bryophytes  and  Pteridophytes  we  find  by  searching,  but 
spermatophytes  fill  the  landscape. 

Like  the  preceding  group  they  present  utmost  diversity 
in  form  and  appearance  and  only  agree  in  a  few  fundamen- 
tals of  life  history.  The  gametophyte  phase  is  so  reduced 
and  difficult  of  study  that  we   will  suit  our  convenience  by 


ORGANIC  EVOLUTION 


143 


Fig.  89.     Chickweed. 


beginning  with  the  sporophyte  phase — the  leafy  plant, 
which,  as  with  the  preceding  group,  is  the  phase  we  ordi- 
narily see. 

Any  familiar  herb,  like  the  chickweed 
(fig.  89),  will  show  how  much  the 
sporophytes  of  the  two  groups  have  in 
common.  The  ordinary  differentiation 
of  the  plant  body  into  root  stem  and  leaf 
is  already  very  familiar.  The  plant 
body  is  covered  over  with  epidermis, 
some  of  whose  cells  develop  in  the  air 
into  plant  hairs  and  in  the  soil  into  rhiz- 
oids.  If  we  strip  a  bit  of  epidermis  from 
a  leaf  we  find  its  constituent  cells,  and 
the  guard  cells  of  the  breathing  pores  to 
be  of  the  same  type  as  in  the  fern  leaf. 
If  we  section  the  leaf  (fig.  90),  we  find 
the  same  tissues  in  the  same 
relations.  There  are  stoma- 
tes  in  both  layers  of  epi- 
dermis and  there  are  inter- 
communicating air  spaces 
throughout  the  interior  of 
the  leaf  and  here  and  there 
are  minute  vascular  bundles 
in  the  midst  of  the  paren- 
chyma. 

In  a  cross  section  of  the 
stem  there  appear  some 
differences  of  importance. 
Epidermis  covers  it  (fig.  91a)  and  parenchyma  fills  most 
of  the  interior  as  before,  but  the  arrangement  of  the 
vascular  bundles  is  very  different.  There  is  hardly  any 
development  of  supporting   tissue  outside  of  the  vascular 


Fig.  90.  Cross-section  of  a  bit  of  chick- 
weed  leaf,  p,  p.  p,  pores;  e,  epidermis; 
X,  crystal  (probably  of  oxalate  of  lime). 


144 


GENERAL  BIOLOGY 


bundles,  and  even  these  are  very  weak  in  a  prostrate 
herb  like  the  chickweed.  The  bundles  are  arranged 
in  a  ring  around  a    central     core    of    parenchyma    (the 


Fig.  91.  Diagrams  of  stem  sections  (exogens).  a,  cross-section  of 
chickweed  stem,  the  inner  circle  representing  the  cambium  ring, 
the  two  radial  lines  indicating  the  portion  enlarged  in  b', 
e,  epidermis;  /t,  hair;  c,  cambium  separating  between  p,  phloem 
and  w,  woody  portions  of  bundles;  v,  spiral  vessels  in  the 
woody  portion;  x,  pith  and  y,  common  parenchyma  of  bark;  c, 
segment  of  a  sunflower  stem;  p,  parenchyma;  6,  bast  fibres;  s, 
sieve  tube;  c,  cambium;  g,  vessels,  pitted  and  spiral;  h,  wood 
fibres,  (from  Wettstein) ;  d,  one  year,  and  e,  four  year  old  woody 
stems,  illustrating   the   increase  of    vascular  bundles. 


ORGAxNIC   EVOLUTION  145 

pith  or  medulla),  and  each  is  divided  by  a  thin  sheet  of 
growing  tissue  known  as  cambium.  Cambium  divides  the 
stem  as  a  whole  into  outer  and  inner  portions  that  are 
familiar  to  every  one  who  has  peeled  a  rod  or  made  a  willow 
whistle ;  we  know  them  as  bark  and  wood.  The  cambium 
divides  each  bundle  into  an  inner  woody  portion  {xylem), 
containing  the  open  vessels  for  conduction  of  water,  and  an 
outer  bast  portion  {phloem)  containing  the  sieve  tubes,  etc. 
There  is  scarcely  any  development  of  bast  fibres  in  the 
chickweed,  and  the  water  conducting  elements  of  the  xylem 
are  spiral  vessels. 

Cambium.^The  most  important  new  feature  is  this  incon- 
spicuous growth  layer  that  divides  the  bundles.  It  forms 
a  sheath  of  thin  cells  that  are  rich  in  protoplasm  and  that 
have  retained  their  capacity  for  further  division.  Cell 
increase  in  the  fern  stem  may  occur  only  at  the  stem  apex. 
When  the  stem  is  once  formed  and  when  its  constituent  cells 
are  fully  grown,  no  further  increase  in  its  diameter  is  possi- 
ble, but  the  cambium  makes  possible  a  continuance  of 
stem  growth.  Hence  the  plants  that  dominate  the  earth  by 
reason  of  their  size,  the  trees  of  the  forest,  all  have  this 
means  of  perennial  growth. 

The  cambium  adds  new  cells  during  each  growing  season 
to  each  of  the  layers  it  separates,  and  the  growth  of  these 
cells  stretches  the  bark  when  it  is  young,  and  when  it  is  old 
and  inelastic,  cracks  it  and  furrows  it,  or  causes  it  to  shed  in 
strips. 

Wood. — Increase  of  size  of  aerial  plant  body  necessitates 
increase  of  supporting  structures,  for  the  long  reach  of  a 
stem  into  a  position  favorable  for  getting  sunlight  would  be 
of  no  use  unless  the  position  could  be  maintained.  Rigidity 
of  stem  in  plants  having  the  manner  of  growth  we  have  just 
been  describing  is  secured  by  further  development  of  the 
woody  elements  of  the  vascular  bundles,  by  increase  in 


146  GENERAL     BIOLOGY 

number  of  the  bundles  and  by  their  consolidation  in  a  ring 
of  wood  underlying  the  cambium.  This  will  be  understood 
from  a  study  of  the  stem  of  any  woody  plant,  such  as  the 
box  elder  (fig.  92).     The  cambium  is  more  abundant,  and 


Fig.  92.  Segment  of  a  four  year  old  woody  stem, 
with  bark  in  part  removed  (b);  c,  cambium;  p, 
pith;  /,  2,  s,  4,  wood  of  the  four  years  growth; 
vertical  surface  shows  wood  fibres  overlaid  by 
transverse  fibres  of  the  medullary  rays. 

clearly  delimits  bark  and  wood.  In  the  bark  there  is  a 
copious  development  of  bast  fibres,  that  protect  underlying 
protoplasmic  parts  (fig.  ()ic).  The  vessels  of  the  wood  are 
pitted  vessels,  and  not  spiral;  and,  most  striking  of  all, 
the  bundles  are  very  numerous  and  very  closely  crowded 
together.  Obviously  such  weak  and  isolated  vessels  as 
those  of  the  chickweed,  while  capable  of  conducting  water, 
are  of  little  use  for  support. 

The  pitted  vessels  constitute  the  frame  work  around  which 
is  built  the  woody  skeleton  of  the  box  elder  tree.  Wood,  as 
we  ordinarily  know  it,  is  composed  of  these  vessels  and  of 
wood  fibres,  and  wood  fibres  are  made  out  of  the  paren- 
chyma cells  which  we"  have  hitherto  seen  forming  the  pack- 
ing around  and  between  the  bundles.  The  cells  lying  be- 
tween the  vessels  become  elongated,  lignified  in  their  walls 


ORGANIC   EVOLUTION  147 

and  consolidated  by  their  over-lapping  pointea  ends  and 
form  the  longitudinal  wood  fibres.  The  cells  lying  between 
the  bundles  become  transversely  elongated,  and  form  the 
wood  fibres  of  the  medullary  rays.  Thus,  there  is  formed 
beneath  the  cambium  a  ring  of  wood,  that  owes  its  solidity 
to  the  close  adhesion  of  cells  having  lignified  walls,  and 
the  beauty  of  its  grain  to  the  arrangement  of  the  cell 
groups. 

The  annual  rings  of  wood  are  formed  by  the  development 
of  vessels  of  larger  diameter  in  the  "spring  wood"  fornxxl 
during  the  early  part  of  the  grooving  season.  As  new  layers 
of  wood  are  added  outside,  those  first  formed  become 
changed  from  "sap  wood"  into  "heart  wood,"  losing  their 
capacity  for  conducting  water.  That  the  heart  wood  is  rot 
essential  to  the  life  of  the  tree,  every  hollow  tree  testifies. 
That  the  outer  layers  are  essential  is  shown  by  the  fatality 
of  "girdling"  the  trunks  by  cutting  a  groove  through  the 
sapwood  and  bark. 

Monocotyledons. — There  is,  however,  one  great  group  of 
seed  plants,  known  as  the  Monocotyledons,  that  has  not  the 
mode  of  growth  above  described.  Structurally  these  are 
much  more  like  the  pteridophytes.  They  have  no  cambium 
ring,  and  no  axis  of  solid  wood,  but  their  bundles  are  scat- 
tered through  a  soft  internal  parenchyma,  and  the  chief 
support  of  the  stem  is  a  stiffened  cortex  beneath  the  epi- 
dermis, comparable  to  the  layer  similarly  situated  in  the 
rhizome  of  the  fern  (fig.  93). 

These  are  the  grasses  and  sedges,  the  lilies  and  irises,  and 
most  other  plants  that  have  parallel  veined  leaves.  These 
dominate  considerable  portions  of  the  earth's  surface,  in 
prairies,  steppes,  savannas,  marshes,  and  other  unforested 
regions.  In  temperate  climes  the  aerial  stems  of  all  of 
them  are  of    annual  growth,   and  the  perenniel  roots  and 


148 


GENERAL   BIOLOGY 


Fig.  93.  Cross  section  of  com 
stalk,  c,  cortical  layer;  v, 
vessels  scattered  through 
the  parenchyma. 


under  ground  stems  of  the  dominant  species  are  not  in- 
jured by  fires  that  would  hinder  forest  growth. 

From  this  very  brief  sketch  of 
the  seed-plant  sporophyte  we  may 
learn  that  the  parts  of  the  plant 
body  are  much  the  same  as  were 
found  in  pteridophytes — -only 
modified  in  form  and  arrange- 
ment. Rhizoids  and  chlorophyl 
bearing  cells  are  the  foraging 
agents  still,  and  vascular  bun- 
dles, the  means  of  communication 
between  them. 

Development. — When  we  turn 
to  the  developmental  side  the 
differences  are  much  greater. 
Flowers  appear  in  the  sperma- 
tophytes,  and — what  is  vastly  more  important — seeds, 
also.  We  have  already  seen  (Chapter  I)  something  of  the 
variety  of  floral  structure.  We  know  that  the  purpose  of 
the  flower  is  to  produce  seed.  Let  us  now  study  the  manner 
in  which  seeds  are  developed. 

Figure  94  shows  at  a  the  flower  of  the  chickweed  with  its 
three  stigma-tips  alternating  with  three  small  stamens,  and 
with  five  small  white  bifurcated  petals  wholly  encompassed 
by  a  like  number  of  big  green  sepals.  At  h  in  the  figure, 
surrounded  by  the  persistent  sepals  and  surmounted  by  the 
stigmas,  is  shown  the  maturing  fruit,  within  which  the  seeds 
are  contained. 

The  differences  between  flowers  of  this  type  and  the 
pteridophyte  in  reproductive  methods  are  so. great,  that  we 
will  find  it  easier  to  study  first  the  conditions  found  in  a  more 
primitive  seed  plant,  and  afterward,  those  found  in  a  highly 
developed  flower.  So  let  us  examine  first  the  pine,  and 
after  that  the  violet. 


ORGANIC  EVOLUTION 


149 


Reproduction  in  the  pine. — In  the  pine  we  again  meet  with 
two  kinds  of  spores,  microspores  and  macrospores.  With 
the     microspores     of     the    seed  plants  we    have  already 

become  acquainted 
under  their  older 
name  of  pollen 
grains,  and  with 
the  microsporan- 
gia,  as  the  pollen 
sacs  of  the  anth- 
ers. The  latter  are 
developed  in  pairs 
in  the  lateral  mar- 
gins of  scales  of 
the  well  known 
little  cones,  which 
shower  down  yel- 
low pollen  in  early 
spring.  Such  cones  are  remotely  comparable  to  the  fruit- 
ing spikes  of  Selaginella  and  Equisetum. 

The  microspore  or  pollen  grain  develops  into  a  male 
prothallium  or  gametophyte  of  extremely  small  size,  con- 
sisting when  grown  of  only  a  few  cells,  one  of  which  on 
division  gives  rise  to  two  sperm  nuclei.  These  lack  loco- 
motor organs  and  do  not  swim  abroad  when  mature ;  instead, 
the  microspore  (or  the  prothallium  developed  from  it)  is 
transported  bodily  by  the  wind  to  the  vicinity  of  the  egg 
cells. 

The  macrospores  (fig.  95)  are  developed  in  similar  fruiting 
spikes,  which  when  mature  are  the  familiar  cones  of  the 
pines  (and  other  conifers).  There  are  but  two  sporangia 
upon  the  base  of  each  scale  and  in  these  the  macrospores 
are  developed  singly.  As  in  selaginella  they  are  of  large 
size,  owing  to  the  food  stored  in  them.     They  differ  from 


Fig.  94.     Chickweed.     a,  flower;  b,  fruit. 


ISO 


GEXERAL   BIOLOGY 


those  of  selaginella  most  markedly  in  not  being  discharged 
at  maturity.  They  remain  permanently  inclosed  in  the 
macrosporangium  (usually  known  in  botany  by  its  older 
name  micellus),  and  invested  closely  by  a  thin  layer  of 
integument,  the  whole  structure  being  known  in  botany  as 
the  ovule. 

The  investing  integument  does  not  close  completely  over 
the  macrosporangium,  but  leaves  a  little  hole  at  one  end, 
the  micropyle.  Hither  the  microspore  is  brought  by  the  wind 


a 

Fig.  95.  Diagrams  of  spore  development  in  the  pine,  a,  longitudinal  sec- 
tion of  the  staminate  small  cone  b,  one  of  the  scales  from  the  same, 
showing  at  c,  the  pollen  cavities  (microsporangia) ;  c,  the  single  pollen 
grain,  divided  into  two  cells,  and  bearing  a  pair  of  thin  flat  winged 
processes  at  its  sides;  d,  a  scale  from  the  pistillate  cone,  bearing  a  pair  of 
macrosporangia:  (o")  ovules;  e-,  a  single  ovule,  in  section,  with  a  pollen 
grain  lying  inside  the  pollen  cavity  at  the  top;  m,  macrospore;  f,  macro- 
sporangmm  penetrated  by  two  pollen  tubes  (i,  /) ;  two  sperm  nuclei  (m) 
shown  in  one  of  them;  the  macrospore  (nz)  is  developed  into  the  female 
prothallium,  bearing    ar^uegonia  {a,  a)  each  containing  an  egg. 

previous  to  fertilization.  The  macrospore  remains 
thus  in  captivity.  AAlthin  it  develops  a  mass  of  cells 
which  is  the  female  prothallium,  in  the  apex  of  which 
adjacent  to  the  micropyle  several  reduced  archegonia  are 
developed,  and  in  each  of  these  an  egg  nucleus  is  produced. 
The  microspore,  previously  lodged  at  the  micropyle, 
develops  a  rhizoid-like  process  (the  pollen  tube)  from  the 
antheridial  cell,  and  this  penetrates  to  the  egg  and  liberates 


ORGANIC   EVOLUTION 


151 


its  sperm  nuclei  through  its  ruptured  tip.  One  of  these 
unites  with  the  egg  cell,  effecting  fertilization.  Then  the 
embryo  sporophyte  of  the  new  generation  begins  to  develop, 
also  in  captivity,  within  the  wall  of  the  old  macrospore,  and 
at  the  e  pense  of  the  prothallial  tissue  which  now  fills  it. 
As  with  the  pteridophytes  studied,  but  one  embryo  is 
developed;  if  several  eggs  are  fertilized,  one  in  developing 
gains  the  ascendency  and  crowds  the  others  out.  The  form 
of  the  embryo  is  indicated  in  (fig.  g6h). 


I    '9 


7/ 


Fig.  96.  Diagrams  of  development  of  the  seed  in  the  pine,  ff, 
a  single  archegonium,  penetrated  by  the  pollen  tube  (/)  from 
which  the  two  sperm  nuclei  are  liberated,  one  of  them  is  unit- 
ing with  the  egg  nucleus  (o) ;  h,  the  seed;  e,  the  embryo, 
which  develops  from  the  fertilized  egg;  s,  endosperm  (remains 
of  the  gametophyte) ;  /,  the  germinating  seed;  the  sporophyte 
slipping  off  the  old  seed  coat  (5)  after  having  consumed  the 
endosperm  that  was  contained  in  it. 

The  seed. — After  developing  a  little  way  the  embryo  enters 
upon  a  resting  stage,  the  integument  hardens  about  it  into 
a  seed  coat,  and  the  whole  becomes  a  seed,  and  falls  away  to 
resume  its  development  when  it  finds  suitable  conditions 
somewhere  in  the  soil.  The  seed  is  thus  a  composite  struc- 
ture consisting  of  three  parts  of  very  different  nature.  The 
seed  coat  and  macrosporangium  wall  represent  and  are  a 
part  of  the  old  sporophyte ;  the  remains  of  the  prothallial 
tissue  within  (known  as  endosperm)    is  gametophyte,  and 


152 


GENERAL  BIOLOGY 


the  embryo  itself  is  the  new  sporophyte.     If  this  seem  con- 
fusing, the  way  to  make  it  clear  is  to  inquire  what  is  the 

origin  of  each  part.  To  learn 
^vhat  is  gametophyte,  learn  what 
has  developed  from  the  spore. 

The  pine  and  the  violet  repre- 
sent the  two  chief  groups  of 
seed  plants,  whose  most  salient 
characters  are  found  in  flower 
and  fruit.  The  gymnosperms 
(gymnos,  naked  and  sperma 
seed)  bear  the  ovules,  and  later 
the  seeds,  uncovered  upon  the 
surface  of  the  scales.  The  an- 
giosperms  {angios,  a  closed  ves- 
sel, and  sperma  seed)  have  the 
ovules  (or  the  seeds)  included 
within  the  closed  pistil. 

Reproduction  in  the  violet. — 
Many  signs  of  specialization  are 
evident  in  such  flowers  as  vio- 
lets. Their  general  structure 
has  already  been  discussed  and 
illustrated  in  Chapter  I.  We 
are  here  concerned  only  with  the 
phenomena  that  lead  directly  to 
seed  development  . 

The  microspore  (pollen)  de- 
velops a  male  gametophyte  of 
but  two  cells,  and  one  of  these 
is  very  small  (fig.  976) ;  but  from 


Fig.  97.     The  microspores  of  the 

t'^  poUen-t  .tel°^"we't   it  are  derived  the  two  sperm  nu- 
r>VetSopSt'°onrj,o'iie1;   clei.     The  other  develops   when 

tube  in  sugar  solution;  c,  after 
15  minutes;  e,  after  an  hour; 
one  sperm  nucleus  shows  in  /. 


The  other  develops 
it   is   carried  to  the   moist   stig- 
matic  surface  of  the  violet  pistil, 


ORGANIC   EVOLUTION 


153 


into  a  very  long  pollen  tube  (fig.  97).  This  grows  down 
the  style  and  enters  the  niicropyle  of  the  ovule  and  liber- 
ates the  two  sperm  nuclei  (that  have  escaped  from  their 
own  cell  wall)  near  the  egg  nucleus. 


Fig.  98.  Diagrams  of  development  of  the  female  game- 
tophyte  in  the  violet,  p,  a  young  ovule:  /  and  2, 
inner  and  outer  integuments;  m,  micropyle;  n, 
macrosporangium  (nucellus) ;  s,  macrospore;  q,  the 
female  gametophyte  at  the  time  of  fertilization;  p, 
pollen  tube  entering;  e,  egg  nucleus;  x,  two 
synergid  nuclei;  y,  two  endosperm  nuclei;  s,  three 
antipodal  nuclei.      Other  lettering  as  in  p. 

The  macrospore,  which  is  situated  (as  in  the  pine)  within 
the  nucellus,  here- surrounded  by  two  investing  integu- 
ments, develops  by  three  successive  divisions  of  its 
nucleus  into  an  aggregation  of  eight  nuclei  within  a  distend- 
ed cell  wall,  the  w^hole  constituting  the  so-called  embryo 
sac.  The  position  and  names  of  these  are  indicated 
in  the  accompanying  diagram  (fig.  989).  One  of  the 
eight  is  the  egg  nucleus,  and  with  it  one  of  the  sperm 
nuclei  from  the  entering  pollen  tube  fuses.  There  is 
no  archegonial  wall.  The  remaining  cells  represent  the 
body  of  the  female  prothallium,  so  far  as  developed  at 
time  of  fertilization.  Among  these  occur  two  puzzling 
phenomena,  which  render  identity  of  parts  somewhat  un- 


154  GENERAL    BIOLOGY 

certain:  the  antipodal  nuclei  disintegrate  and  the  endo- 
sperm nuclei  fuse  (and  sometimes  the  second  sperm  nu- 
cleus fuses  with  them) ,  before  undergoing  further  division 
to  form  the  endosperm. 

Subsequent  development  is  wholly  comparable  with  that 
of  the  pine  already  discussed,  save  that  in  many  of  the 
higher  spermatophytes  the  endosperm  is  wholly  absorbed, 
and  the  matured  seeds  contain  only  the  embryo,  and  are 
without  endosperm. 

Study  21.     Spermatophyte  structure. 

Materials  needed:  Stems  and  leaves  of  chickweed  or 
other  herbaceous  plant.  Miscellaneous  wood  specimens, 
green  and  finished.  Sections  and  slide  mounts  showing 
vascular  bundle  elements.  Stems  and  leaves  of  monocoty- 
ledons. 

No  specific  program  need  be  given  for  a  single  study  of  a 
subject  that  offers  so  vast  an  array  of  possible  materials. 
Suffice  it  to  suggest  that  the  student  use  whatever  materials 
are  at  hand  as  a  means  of  identifying  in  the  higher  plants 
the  tissues  already  seen  in  the  pteridophytes,  and  to  dis- 
cover the  new  features  of  tissue  arrangement  presented  by 
exogenous  and  endogenous  growth. 

The  record  of  this  study  may  consist  in  a  few  diagrams 
and  a  complete  list  of  the  materials  studied  and  statement 
of  what  they  illustrate. 

Study  22.     Spermatophyte  development. 

Materials  needed:  Flowers  and  flower  buds,  from  which 
to  obtain  ripe  pollen;  sections  of  female  gametophytes; 
seeds  with  and  without  endosperm. 

Study  the  pollen  grains  wet,  dry,  and  germinating  in 
drop  cultures. 

Study  the  enfolding  integuments  in  sections  of  young 
ovules  (fig.  98^) ;   study  the  mature  gametophyte  in  older 


ORGANIC  EVOLUTION 


155 


Fig.  99.  Diagram,  illustrating  alternation  of  generations  in  the 
higher  green  plants.  The  horizontal  lines  of  figures  represent 
(/,  2,  j),  successive  generations;  gametophyte  is  white  and  sporo- 
phyte  is  solid  black;  the  egg  is  represented  by  circle  with  central 
dot,  the  spores  are  represented  by  black  dots,  of  two  sizes  when 
differentiated.  The  types  represented  are:  a,  a  simple  livenv'ort, 
(Riccia) ;  fo,a  more  specialized  liverwort,  (Conocephalus) :  c,  a  moss; 
0,  a  fern;  e,  a  horsetail;  /,  Selaginella  and,  g,  a  seed  plant  (seed 
in  (  ) -marks,  above). 


156  GENERAL  BIOLOGY 

sections,  and  also  the  developing  embryo,  and  diagram. 
Germinate  the  seeds  and  trace  the  disappearance  of 
the  endosperm. 

The  record  of  this  study  may  consist  in  notes  on  and 
diagrams  of  the  principal  things  observed. 

The  gametophyte  phase  of  the  higher  seed  plant  is  well 
nigh  suppressed  :*  why,  we  cannot  say.  And  sex  charac- 
ters, w^hich  primarily  must  belong  to  the  sexual  phase, 
are  gradually  extended  to  the  sporophyte:  first  to  the 
spores  alone,  then  to  the  sporangia  and  flower  scales  and 
finally,  in  unisexual  (dioecious)  species,  to  the  whole 
organism. 

The  great  advance  made  by  the  spermatophytes  over  the 
lower  groups  is  in  their  manner  of  reproduction.  Bryo- 
phytes  and  Pteridophytes,  though  terrestrial,  have  retained 
an  aquatic  mode  of  fertilization.  Their  free  swimming  sperms 
are  subject  to  vicissitudes  of  drouth  which  the  seed  plants 
have  largely  obviated.  The  weak  point  in  the  life  history 
of  the  fern  is  in  the  development  of  delicate  unprotected 
prothallia  from  microscopic  spores.  The  seed  plant  sets  its 
offspring  adrift  only  when  grown  to  considerable  size  and 
supplied  with  a  store  of  food  material  for  further  growth. 
What  chance  of  a  living  have  fern  spores  in  competition 
with  seeds  ?  A  main  reason  for  the  dominance  of  the  seed 
plants  upon  the  earth  in  our  own  time  therefore  lies  in  the 
better  start  in  life  they  furnish  to  their  offspring. 

II.       THE    ANIMAL    SERIES. 

We  will  choose  among  the  higher  animals  a  series  of  forms 
ending  with  the  vertebrates,  and  will  illustrate  it  with  three 
types: — hydra,  the  earthworm  and  salamander,  with  some 
supplemental  illustrations  drawn  from  the  vertebrate  group. 

*The  accompaning  diagram  (fig.  99)  is  offered  as  an  aid  to  the 
beginning  student  who  may  still  find  difficulty  in  identifying  its 
remains. 


ORGANIC  EVOLUTION 


157 


THE    HYDRA. 

This  is  a  transparent  aquatic  animal  about  half  an  inch 
long  that  lives  attached  to  stems  and  leaves  in  ponds  and 
sluggish  streams.  It  has  a  slender  tubular  body,  provided 
with  a  disc-like  foot  at  its  basal  end  for  attachment,  and  a 
circlet  of  tentaaes  surrounding  a  mouth  at  the  other  end. 
Both  body  and  tentacles  are  very  contractile,  and  become 
suddenly  drawn  down  into  a  heap  upon  disturbance.  On 
this  account,  although  it  is  immensely  larger  than  the  ani- 
mals studied  hitherto,  it  is  difficult  to  see  while  collecting  in 
the  field.  If  stems  on  which  it  is  sought  be  placed  in  a 
shallow  white  dish  of  water,  or  in  a  glass  vessel  to  be  viewed 
toward  the  light,  it  may  be  seen  when  it  extends  itself  again 
after  a  few  minutes,  undisturbed.  It  is  likely  to  be  present 
on  loose  trash  lying  in  any  pond  or  slow  stream,  and  a  good 
way  to  find  it  is  to  bring  in  a  pailful  of  this  trash  and  distrib- 
ute it  in  aquarium  jars  to  stand  over  night.      If  present  in 

numbers  mxany  of  the  hydras 
will  move  out  upon  the  glass 
on  the  lighted  side  of  the  jar 
where  they  may  be  readily 
seen  on  looking  toward  the 
light.  Too  much  trash  in  a 
single  jar  will  obscure  the 
view,  of  course.  Specimens 
may  be  transferred  to  a 
watchglass  or  slide  for  study 
by  scraping  them  loose  from 
their  support,  and  taking 
them  up  in  a  pipette,  or  bet- 
ter in  a  tube  attached  to  a 
hand  bulb. 

In   the   aquarium   hydras 
may  be  seen  in  any  position, 


Fig.  100.     A  hydra,      a,  extended;  b, 
contracted;  spermary  on  the  body 
above;  o,  ovaries  below. 


158  GENERAL  BIOLOGY 

attached  to  the  glass,  or  to  the  surface  film  of  the  water, 
as  well  as  to  the  stems;  their  bodies  extended  up  or  down 
or  sidewise;  their  tentacles  extended  radially  around  the 
mouth.  If  fully  extended,  the  tips  of  the  tentacles  hang 
vertically  in  the  water  and  are  excessively  slender.  These 
are  hydra's  fishing  lines,  set  for  passing  water  fleas,  minute 
worms,  etc.,  which  they  paralyze  by  contact;  contracted, 
they  are  its  arms,  and  are  used  for  pushing  the  paralyzed 
prey  into  its  mouth.  Feeding  is  so  slow  a  process,  however, 
that  if  one  be  so  fortunate  as  to  see  the  prey  captured  he  is 
likely  to  have  to  watch  some  time  to  see  it  swallowed. 
Often  the  body  is  seen  to  be  roundly  distended  in  places  by 
previously  ingested  food  in  proce'ss  of  digestion. 

The  hydra  moves  from  place  to  place  by  turning  end  over 
end.  It  bends  over  in  the  desired  direction,  rests  its  tenta- 
cles on  its  support,  lifts  its  foot  and  swings  it  over  forward, 
attaches  it  and  rises  again.  If  the  hydra  be  seen  standing 
on  its  tentacles  with  its  foot  in  the  air,  it  is  in  the  midst  of 
one  of  these  turns,  wdiich  are  made,  not  like  hand  springs, 
but  with  very  great  slowness.  By  this  means  it  migrates 
to  the  lighted  side  of  the  jar.  It  also  moves,  but  more 
slowly,  by  alternate  contractions  and  expansions  of  its  foot : 
a  sort  of  creeping  progression. 

When  a  number  of  hydras  are  present  in  an  aquarium, 
some  of  them  are  likely  to  show  buds  growing  out  from  the 
side  of  the  body.  If  several  well  grown  buds  be  present  on  a 
single  individual  they  make  it  appear  somewhat  more 
"hydra  headed,"  since  on  the  divided  body  there  are  then, 
if  not  heads,  at  least  divergent  tentacled  tips.  The  buds, 
however,  separate  before  they  attain  the  full  size  of  the 
parent.  Their  development  may  be  traced  in  stages  found 
in  different  individuals.  First,  there  is  an  outpushing  of  the 
body  wall  in  a  little  rounded  knob;  this  elongates  into 
tubular  form ;     there  it  develops  a  whorl  of  tentacles  that 


ORGANIC  EVOLUTION 


159 


first  appear  as  a  circle  of  rounded  knobs  about  the  free  end, 
and  later  elongate.  A  mouth  breaks  through  at  the  distal 
end  of  the  body,  and  finally,  the  base  constricts  itself  off, 
closing  communication  with  the  internal  food  cavity  of  the 
parent,  and  develops  a  foot  for  independent  attachment. 
Then  the  little  hydra  drifts  away  to  set  up  in  business  on  its 
own  account.  This  is  obviously  an  asexual  process  of 
reproduction. 

The  sexual  process  is  not  so  often  observable.  The  sexual 
organs,  when  present  appear  as  minute  transparent  swellings 
on  the  surface  of  the  body;  conical  and  situated  above  the 
middle,  if  spermaries;  low  and  broadly  domeshaped  and 
situated  nearer  the  foot,  if  ovaries. 


^   f^^^ 


Fig.  101.  Hydra,  a,  a  sperm  cell;  b,  an  egg  cell;  c,  diagram  of  a 
longitudinal  section  of  the  body,  bearing  a  lateral  bud,  ectoderm 
white,  endoderm  black;  d,  a  bit  of  the  body  wall  showing  tissue 
layers;  e,  dissociated  cells  with  basal  contractile  processes;  /,  a 
rudimental  nerve  cell. 

If  a  hydra  be  transferred  to  a  slide  or  watchglass  and 
examined  a  little  magnified,  the  two  constituent  layers  of  its 
body  wall  may  readily  be  made  out;  a  transparent  outer 
ectoderm,  and  a  darker  inner  endoderm.  The  endoderm 
lines  the  food  cavity,  which  is  merely  a  blind  sac  having  only 
one  opening,  the  mouth,  through  which  food  is  taken  in  and 
its  indigestible  residue  is  thrown  out.  The  tentacles  being 
formed  by  outgrowth  of  both  layers  are  hollow,  each  is  a 
similar  smaller  blind  sac  opening  into   the   major   cavity. 


i6o  GENERAL  BIOLOGY 

This  very  simple  plan  of  structure  is  indicated  in  the  accom- 
panying diagram  (fig.  loi). 

The  body  of  the  hydra  is  too  large  for  the  satisfactory 
study  of  the  form  and  relations  of  its  constituent  cells  in  the 
living  animal.  The  two  cell  layers  are  easily  made  out,  and, 
in  the  slender  and  transparent  tip  of  an  extended  tentacle, 
some  large  nettling  cells  (nematocytes)  are  readily  observ- 
able. These  contain  transparent  ovoid  sacs  {nematocysts) 
(fig.  102)  occupying  slight  elevations  of  the  ectoderm  of 
the  tentacle.  Inside  each  nematocyst  is  a  closely  coiled 
stinging  filament,  which  when  discharged  in  contact  with  a 
waterflea,  paralyzes  it  and  prevents  its  escape.  Close  be- 
side each  nematocyst  is  an  erect  minute  sensory  point, 
which  when  touched  by  the  water-flea,  communicates  the 
stimulus  that  causes  the  discharge  of  the  filament.  This 
discharge  may  be  caused  artificially,  while  one  is  watch- 
ing, if  some  irritating  fluid,  like  dilute  acetic  acid,  be 
run  under  the  coverglass  that  confines  the  hydra  upon 
a  slide.  By  keeping  one's  eye  at  the  microscope  while 
the  acid  is  diffusing  under  the  cover  until  it  comes  in 
contact,  some  of  the  nematocysts  will  be  seen  to  be  thrown 
out  bodily,  while  others  will  throw  out  only  their  filaments, 
which  will  then  hang  like  long  flexuous  transparent  hairs  to 
the  side  of  the  tentacle. 

The  cellular  structure  of  the  hydra  is  made  out  by  the 
study  of  thin  sections  and  of  macerated  preparations  of  dis- 
sociated cells.  In  a  cross  section  of  the  body,  ectoderm  and 
endoderm  stand  out  with  diagrammatic  clearness.  Their 
constituent  cells  are  seen  to  be  considerably  differentiated, 
those  of  the  endoderm  being  rather  larger,  and  variously 
shaped  at  their  free  internal  ends,  where  some  bear  flagella, 
and  others  pseudopodia.  Digestion  in  the  hydra  combines 
the  methods  of  the  lower  animals  hitherto  studied,  in  which 
the  food  is  engulfed  by  the  protoplasm  and  digested  within 


ORGANIC  EVOLUTION  i6i 

the  cell,  with  that  of  the  higher  animals,  in  which  the  food  is 
digested  in  a  stomach  through  the  action  of  fluids  poured  out 
by  the  cells  and  afterwards  absorbed.  Individual  cells  of 
the  endoderm  of  the  hydra  digest  minute  diatoms,  etc.,  after 
the  former  method;  the  endoderm  collectively  digests 
water-fleas  and  the  larger  kinds  of  prey  after  the  latter 
method. 

The  ectoderm  is  a  composite  layer,  especially  in  the  upper 
part  of  the  body,  consisting  of  larger  cells  that  form  the 
surface  layer,  and  taper  down  to  their  inner  ends,  and  smaller 
interstitial  cells  that  fill  the  spaces  between  the  bases  of 
larger  cells,  but  do  not  reach  to  the  outside.  These  inter- 
stitial cells  grow  up  to  the  surface  and  some  of  them  develop 
there  into  nematocytes  by  a  remarkable  differentiation  of 
the  cytoplasm  of  their  upper  ends.  It  is  probable  that 
after  the  discharge  of  the  nematocysts,  other  of  the  inter- 
stitial cells  act  as  replacement  cells,  growing  up  and  pro- 
ducing   new    ones. 

There  is  a  significant  development  of  the  base  of  the 
ectoderm  cells  that  can  only  be  made  out  well  if  the  tissues 
be  dissociated  so  that  the  cells  may  be  viewed  singly.  In 
such  a  preparation,  many  of  the  ectodermal  cells  are  seen 
to  have  long  slender  processes  extending  lengthwise  of 
the  body  beneath  the  ectodermal  layer  in  physical  contact 
with  many  of  its  cells  (fig.  loi  e).  It  is  believed  that  these 
processes  are  especially  contractile,  and  that  they  account 
for  the  ability  of  the  body  as  a  whole  to  shorten  so  rapidly 
when  disturbed.  These  foreshadoAV  the  muscles  of  the 
higher  animals.  Other  cells  of  the  form  shown  in  figure  loi 
are  also  present  among  these  processes  and  appear  to  be 
primitive  nerve  cells,  serving  to  communicate  the  stimuli 
and  to  secure  simultaneous  contraction  of  all  the  cell  pro- 
cesses of  the  whole  layer,  securing  concerted  and  coordinated 
action. 


l62 


GENERAL  BIOLOGY 


The  hydra  is  a  large  and  fairly  well  integrated  body  of 
cells,  among  which  division  of  labor  is  very  obvious.  Clear- 
ly the  digestion  and  absorption  of  food  must  fall  to  the 
endoderm  cells,  which  alone  come  into  contact  with  it. 
Likewise,  the  protection  of  the  body  and  responses  to  stimuli 
from  without  must  fall  to  the  ectoderm  cells.  The  function 
of  the  nettling  cells  is  much  more  specialized. 

Both  spermaries  and  ovaries  develop  in  the  ectoderm, 
each  as  a  little  mass  of  cells  covered  by  a  thin,  transparent 
ectodermal  film. 

In  the  spermary,  each  included  cell  develops  a  motile 
sperm  which  when  mature  may  be  seen  actively  swimming 
about  in  the  transparent  conical  tip  of  the  spermary  of  the 
living  hydra.  Of  the  cell  mass  which  is  to  be  the  ovary, 
one  cell  gains  the  ascendency  and  grows  at  the  expense  of 
the  others,  absorbing  their  contents  and  storing  up  reserve 
food  materials.  This  cell  which  when  mature  is  the  egg, 
has  the  singular  amoeboid  appearance  shown  in  figure  loi  b. 

At  maturity  the  top  of  the  ovary 
bursts,  making  a  passage  for  the 
ingress  of  the  sperms,  and,  in  fer- 
tilization, one  of  these  fuses  with 
the  egg  cell. 

Study    2j.      Observations    on    the 
structure  of  the  hydra. 

Materials  needed:  Living  hy- 
dras of  any  species;  budding 
individuals,  and  also  others  bear- 
ing   the    sex    organs.     Mounted 

Fig.  102.    Nettling  cells  of  the  ^ross   scctions  of  the  body,  and 
hydra,     a.  charged;  b,  dis-    dissociation  preparations  of  ecto- 

charged.  ^      ^ 

derm  cells. 
Study  these  things  in  the  order  mentioned,  using  the 
foregoing  account  of  the  hydra  as  a  basis  of  observations. 


ORGANIC  EVOLUTION  163 

The  record  of  the  work  done  may  consist  in  the  following 
figures : 

1.  Positions  of  hydra  at  rest,  and  form  of  body  extended 
and  contracted. 

2.  Buds  in  various  stages  of  development. 

3.  Sexual  organs,  if  found,  and  the  sex  cells  if  these  can 
be  made  out. 

4.  Nematocysts  in  the  tentacle,  and  the  same  discharged. 

5.  Cross  section  of  the  body,  drawn  from  section. 

6.  Diagram  of  a  longitudinal  section  of  body. 

THE    EARTHWORM.* 

To  every  one  who  turns  the  soil  in  flower  bed  or  garden 
this  animal  is  very  familiar.  It  assists  in  tillage  by  perforat- 
ing the  soil  with  its  burrows,  and  by  carrying  subsoil  up 
from  below  in  the  "castings"  which  it  strews  around  the 
mouth  of  its  burrow,  and  mixes  with  the  humus.  Being 
nocturnal  and  blind,  its  activities  may  be  easily  observed 
with  a  lantern  on  a  wet  night,  when  it  will  be  found  partly 
extended  from  its  burrow,  reaching  about  over  the  soil  from 
its  doorway,  ever  ready  to  make  a  quick  retreat  if  disturbed. 
If  seized  quickly  and  held  for  a  moment  until  it  releases  its 
hold  on  the  walls  of  its  burrow,  it  may  then  be  pulled  out  of 
it;     this  is  the  way  to  get  specimens  for  study. 

External  features. — The  body  of  the  worm  is  segmented: 
i.  e.,  it  consists  of  a  series  of  transverse  rings  or  segments 
(somites).  There  is  no  head  and  no  tail,  but  there  are 
definite  front  and  hind  ends.  At  the  former  is  the  mouth, 
overhung  by  a  muscular  flap  or  fold,  the  prostomiuni, 
which,  in  absence  of  arms  or  tentacles,  assists  in  getting  food 
into  the  mouth ;  at  the  other  end  is  the  anus ;  and  the  ali- 
mentary canal  extends  straight  through  the  middle  of  the 
body  from  end  to  end 


*The  following  outlines  apply  especially  to  the  lar^e  Lumbricus 
herculeus,  which,  on  account  of  its  size,  is  a  favorable  form  for  dis- 
section 


1 64 


GENERAL  BIOLOGY 


The  ventral  surface  of  the  worm  is  somewhat  flattened, 
and  at  either  side  of  it  are  two  double  rows  of  minute  setae 
with  their  tips  protruding  through  the  skin.  They  are 
short  and  stiff,  and  not  at  all  conspicuous — indeed,  are 
easier  felt  than  seen,  as  one  may  demonstrate  by  drawing  a 
worm  backward  between  the  thumb  and  finger.  It  is  by 
means  of  these  that  the  worm  maintains  its  footing  in 
crawling,  or  its  hold  within  its  burrow. 

The  only  conspicuous  external  feature  is  the  broad  girdle 
or  clitellum  that  surrounds  the  body  between  the  thirtieth 
and  fortieth  segments.  Although  inconspicuous, the  openings 
of  the  ducts  from  the  reproductive  organs  may  be  seen  at  the 
sides  of  the  ventral  surface  of  segments  fourteen  and  fifteen, 
between  the  rows  of  setae. 

Internal  Features. — The  body  of  the  hydra  is  tubular  in 

plan;  that  of  the 
worm  is  compound- 
tubular — a  tube  with- 
in a  tube;  the  inner 
tube  is  the  food  tube, 
alimentary  canal  or 
enteron;  the  outer  is 
the  body  wall;  the 
space  between  is  the 
body  cavity  or  cceloni 
(see  fig.  103). 

If  a  worm  be  anes- 
thetized with  chloro- 
form, and  a  slit  be 
made  through  the 
body  wall  along  the 
mid-dorsal  line,  and  the  cut  edges  be  drawn  apart  for 
inspection  of  the  interior,  it  will  at  once  be  seen  that  the 
segmentation  of  the  worm  extends  to  the  internal  organs — 


ni,^iiii/iiHiniim/nniriiM 


Fig.  103.  Diagrams  of  the  structure  of  hydra  and 
worm,  a,  cross,  and  b,  long-sections  of  hydra; 
c  and  d,  corresponding  sections  of  the  worm. 
The  ectoderm  is  stippled,  the  endoderm,  solid 
black  and  the  mesoderm  of  the  worm,  cross- 
lined;  o,  coelom. 


ORGANIC  EVOLUTION  165 

that  segments  of  the  worm  are  delimited  internally  by  thin 
transverse  membranous  partitions  or  septa,  which  divide 
the  coelom  into  a  series  of  compartments,  within  which 
certain  structures  are  serially  repeated.  At  the  middle  of 
the  body  these  structures  are  typically  seen.  The  large 
enteron  occupies  the  center  of  the  body.  A  slender  vessel 
of  bright  red  color  extends  along  its  dorsal  side.  This  is  the 
dorsal  vessel,  the  central  part  of  a  blood  vessel  system.  Its 
color  is  due  to  the  contained  blood,  which  it  drives  forward 
by  evident  pulsations  of  its  walls.  It  is  joined  in  every  seg- 
ment by  small  lateral  paired  blood  vessels,  some  of  which 
may  be  traced  to  the  body  wall  and  some  to  the  walls  of  the 
enteron.  If  the  septa  be  cut  for  a  little  way  on  one  side, 
and  the  alimentary  canal  be  pushed  over  to  the  other  side, 
another  smaller  longitudinal  blood  vessel,  the  sub-mtestinal, 
may  be  seen  extended  lengthwise  beneath  it.  In  this  the 
flow  of  the  blood  is  toward  the  rear.  In  the  seventh  to 
eleventh  segments  of  the  body  there  are  large  paired 
strongly  contractile  vessels,  the  aortic  arches,  extending 
downward  each  side  joining  the  dorsal  vessel  to  the  sub- 
intestinal. 

Nervous  system. — On  the  floor  of  the  body  cavity  beneath 
the  sub-intestinal  vessel  lies  the  white  nerve  cord,  from 
which  slender  branching  nerves  arise  in  every  segment.  In 
the  foremost  segment  of  the  body  this  cord  divides  into  two 
commissures  which  pass  one  on  either  side  of  the  enteron, 
and  reunite  above  it  in  a  mass  of  nervous  tissue  that  is  the 
brain  or  cerebral  ganglion.  From  the-  brain  arise  nerA'cs 
that  pass  into  the  prostomium  and  into  the  walls  of  the 
enteron. 

The  food  tube  or  enteron. — This  canal  is  differentiated  at 
its  anterior  end  into  a  series  of  organs.  Immediately  behind 
the  mouth  is  a  muscular  pharynx.  The  circular  muscles  of 
tis  walls  contract  it,  and  the  copious  radiating  fibres  that 


i66  GENERAL  BIOLOGY 

extend  outward  on  every  side  to  the  body  wall,  expand  it, 
making  it  an  efficient  organ  for  sucking  the  food  into  the 
mouth.  Behind  the  pharynx,  the  esophagus  extends  as  a 
slender  passage-way  leading  to  the  thin  walled  and  disten- 
sible crop,  which  lies  at  about  the  fifteenth  segment  and  this 
immediately  adjoins  the  thick  walled  muscular  chitin-lined 
gizzard,  which  comes  nearest  to  a  grinding  organ  of  any- 
thing possessed  by  the  worm.  The  remaining  part  of  the 
alimentary  canal  is  undifferentiated  stomach-intestine.  In 
this  the  final  digestion  and  absorption  of  the  food  occurs. 
If  the  alimentary  canal  be  slit  open  and  washed  out  (it 
will  evert  itself  in  a  freshly  killed  worm  by  the  contraction 
of  the  circular  muscles  of  its  walls)  a  sudden  change  in 
the  color  of  the  lining  tissues  will  be  seen  at  the  beginning 
of  the  stomach-intestine ,  the  nature  of  which  will  be  indi- 
cated later  when  development   is   considered. 

Nephridia. — In  the  coelom  at  either  side  of  the  enteron 
in  every  typical  segment  will  be  seen  a  delicate  whitish 
organ,  at  first  appearing  like  a  tangle  of  whitish  threads; 
it  is  the  nephridium,  a  simple  excretory  organ,  whose  prin- 
cipal function  is  the  removal  of  nitrogen  waste  from  the  body. 
It  is  a  coiled  and  twisted  tube,  which  opens  into  the  body 
cavity  by  a  funnel-shaped  aperture  lined  with  cilia,  and  to 
the  outside  by  an  excessively  minute  pore  that  is  situated 
near  the  lower  line  of  setae.  The  body  of  each  nephridium 
lies  in  one  segment,  and  the  funnel  aperture  and  short  stalk- 
like beginning  of  the  tube  (which  perforates  the  septum  low 
down  near  the  nerve  cord)  lies  in  the  preceding  segment. 
The  relations  of  the  nephridia  to  the  body  as  a  whole,  and 
to  the  other  internal  organs,  the  principal  trunks  of  the 
circulatory  system,  the  position  of  the  setae  and  of  the 
principal  muscle  bands  are  indicated  in  the  accompany- 
ing diagram  of  a  cross  section  of  the  worm  (fig.  104a). 
The    muscle    system    consists    of    the    broad   outer  sheet 


ORGANIC  EVOLUTION 


167 


Fig.  104.     Diagrams  of  worm  structure,     a.  cross 
section  of  the  bodv  .  e.  food  tube  or  enteron 
c,  coelom .  m,   nephndia;  v.  dorsal  blood   ves 
sels;  m,  ventral  nerve  cord,  with  sub  intestinal 
vessel  above  it   and   subneural  vessel  beneath 
it.  s,  s,  s,  s  setae      b  cross  section  of  the  body 
wall,  h,  hypodermis  or  epidermis,  with  cover- 
ing cuticle;  I    circular  muscle  layer.   7,  longi- 
tudinal   muscle  layer     ^.peritoneum     c  cross 
section  of  a  bit  of  the  wall  of  the  enteron  .  /. 
chloragogue  cells   (modified   peritoneum),    m 
isolated  longitudinal  muscle  fibres;  n,  circular 
muscle  layer      0     blood    spaces;  p,  digestive 
epithelium  (.endodeim). 


of  circular  muscles 
and  the  huge  tracts 
of  longitudinal  fibres 
shown  in  this  diagram 
of  circular  and  longi- 
tudinal fibres  in  the 
walls  of'  the  alimen- 
tary canal,  and  of  a 
set  of  slender  fibres 
attached  to  the  base 
of  each  seta. 

Organs  of  reproduc- 
tion and  sex  cells. — In 
the  region  of  the 
ninth  to  fifteenth  seg- 
ments of  the  body, 
the  most  conspicuous 
parts  seen  are  the  re- 
productive organs 
(fig.  105),  which  are 
of  remarkable  com- 
plexity. The  largest 
of  these  are  the 
sperm  vesicles,  three 
large  white  paired  or- 
gans in  segments  ten 
to  twelve,  increasing 
in  size  posteriorly, 
the  pair  of  the  twelfth 
segment  extending 
backward  at  its  free 
upper  end  into  one  or 
two  of  the  segm.ents 
behind ;  these  are  sep- 


i68 


GENERAL  BIOLOGY 


arate  only  on  the  sides  and  above,  being  united  across  the 
median  Hne  below  the  enteron.  They  contain  the  sper- 
maries,  and  usually  a  large  mass  of  sperm  cells  in  the  later 
stages  of  development  liberated  therefrom.  If  one  slit  open 
a  vesicle  and  take  from  it  a  drop  of  its  whitish  fluid  contents 
and  mount  this  in  a  drop  of  normal  salt  solution  for  the 
micoscope  he  will  see  abundant  sperm  cells.  They 
deverlop  in  berry-Hke  clusters  of  ovoid  cells,  which  gradually 

lengthen  out  into  a  flagellum- 
like  tail  at  their  distal  ends,  and 
finally  break  apart  and  swim 
free.  They  pass  down  the  sperm 
ducts  to  the  external  openings 
already  seen  on  the  ventral  side 
of  segment  fifteen.  Their  first 
destination  is  the  sperm  recep- 
tacles of  another  worm.  These 
receptacles  may  be  seen  on  the 
floor  of  the  body  cavity  at  either 
side  of  the  foremost  sperm 
vesicle,  two  pairs  of  whitish  or 
yellowish  sacs,  whose  outlets  are 
at  front  and  hind  margins  of  seg- 
ment ten. 

The  sperms  are  extruded  in 
copulation,  when  two  worms 
come  together  in  reversed  position,  so  that  the  A'entral  sur- 
faces of  segments  ten  and  fifteen  are  opposed  to  each  other. 
The  sperm  cells  of  each  worm  are  passed  out  and  into  the 
sperm  receptacles  of  the  other  worm.  This  is  preliminary 
to  fertilization. 

The  eggs  are  produced  in  simple  ovaries  that  lie  in  the 
thirteenth  segment,  attached  near  the  nerve  cord  to  the 
septum  in  front.     When  mature  they  break  away  and  lie 


Fig.  105.  Diagram  of  reproduc- 
tive organs  of  the  earth  worm, 
as  viewed  from  above,  the  body 
wall  outspread,  and  the  enteron 
removed.  a,  nerve  branches; 
b,  nerve  cord;  c,  sperm 
receptacles,  d,  d,  d,  sperm  vesi- 
cles; e,  e,  spermaries(two  pairs) ; 
/,  sperm  duct;g,  g,  ovaries;/:,  h, 
oviducts;  i,  nephridium.  Serial 
number  of  segments  indicated 
at  left. 


ORGANIC  EVOLUTION 


169 


free  in  the  body  cavity.  Later  they  enter  the  funnel-shaped 
end  of  a  short  oviduct,  that  penetrates  the  septum  at  the 
rear  of  the  thirteenth  segment,  and  opens  to  the 
exterior  on  the  ventral  surface  of  the  fourteenth  segment,  as 
before  noted. 

A  preliminary  change  in  the  clitellum  precedes  the  dis- 
charge of  the  eggs.  The  glands,  to  which  the  clitellum  owes 
its  thickness,  secrete  a  milky  fluid  within  it  that  loosens  it 
from  the  body.  It  breaks  its  moorings,  and  is  gradually 
worked  forward  and  finally  slipped  off  over  the  front  end. 
Its  front  and  rear  openings  are  elastically  held  close  to  the 
sides  of  the  worm,  retaining  all  its  fluid  content,  into  which 
while  passing  segment  fourteen,  the  eggs  are  discharged,  and 
while  passing  segment  ten,  the  sperms,  also,  stored  there 
previously,  derived  from  another  worm.  Passing  off  at  the 
front,  the  ends  close  elastically,  making  a  cylindric  capsule 

with  pointed  ends.  Within  this  fertili- 
zation takes  place — cross-fertiHzation, 
of  necessity,  and  the  eggs  pass  the  early 
stages  of  their  development  in  the  milky 
fluid  in  which  they  float ;  it  is  for  the 
young  worms  both  cradle  and  food. 
These  capsules  are  left  lying  under 
leaves  on  damp  soil,  into  w^hich,  the 
little  worms  on  emergence  may  enter. 

Thus  the  worm,  like  the  hydra  and 
many  of  the  other  lower  animals  is 
bisexual  (hermaphroditic).  Cross-fer- 
tilization in  the  hydra,  secured  by  the 
earlier  maturing  of  the  sperm  cells  than 
of  the  eggs,  is  in  the  worm  secured  by 
the  complicated  method  just  described.  For  the  sperm  cells 
are  essentially  aquatic;  in  the  water  they  may  reach  the 
egg  unaided,  but  in  order  to  fulfill  their  function  in  terres- 
trial animals  they  require  to  be  transported. 


Fig.  106.  Ovary  and  sex 
cells  of  the  earth 
worm,  s,  sperm;  e, 
egg. 


lyo 


GENERAL   BIOLOGY 


Early  development. — The  cellular  structure  of  the  earth- 
worm is  best  understood  when  considered  in  the  light  of  its 
origin.  The  worm,  like  all  other  organisms  begins  life  as  a 
single  cell.  In  a  broad  sense,  two  processes  make  up  its 
physical  career;  cell  multiplication,  and  cell  differentia- 
tion. The  former  necessarily  precedes;  the  latter  pre- 
dominates during  the  later  stages  of  development,  but  boh 
take  place  concurrently  throughout  life  in  parts  of  the  body. 

The  egg  (fig.  io6  ^)  when  fertilized  is  potentially  a  new 
worm.  Whatever  characteristics  are  to  appear  in  the  adult 
are  already  inherent  in  it.  It  is  isolated  from  further 
parental  influence.     It  develops  of  itself. 


Fig.  107.     Diagrams  of  the  development  of  the  ear<-+h- 
worm,    early  a,  b,  c,    2-cell,    4-cell,   and   8-cell  stages, 
respectively;  d,  e,  f,  sections  of  later  stages   showing 
gastrulation.  and  the   formation  of    the  mesoderm, 
(after  Wilson). 

There  is  nothing  of  the  worm  structure  visible  in  it;  we 
can  see  in  it  only  the  usual  parts  of  a  normal  undifferentiated 
cell — a  nucleus,  cytoplasm,  and  inclusions,  within  the  cell 
wall.  Moreover,  there  is  nothing  suggestive  of  a  worm  in 
the  earlier  of  the  series  of  remarkable  changes  through 
which  it  passes  in  development  (fig.  107).  It  divides  into 
two  cells,  the  two  divide  into  four,  the  four  into  eight,  the 
eight  into  sixteen,  etc.,  by  a  regular  and  nearly  equal  divi- 
sion. This  process  is  com_mon  to  all  animals  above  the  pro- 
tozoans, and  is  called  cleavage  or  segmentation.     It  results 


ORGANIC  EVOLUTION 


171 


in  a  hollow  sphere  of  cells  (fig.  loj  d)  arranged  around  the 
now  distended  wall  of  the  old  egg,  and  called  a  blastula. 
Then  with  the  continued  increase  of  cells  by  fission  the  wall 
of  the  blastula  becomes  pushed  in  on  one  side  like  a  hollow 
rubber  ball  indented  with  the  thumb.  As  the  central  cavity- 
deepens  the  walls  come  closer  together,  and  their  convergent 
edges  form  a  round  opening,  the  blastopore.  In  this  two- 
layered  body  we  may  already 
recognize  ectoderm  and  en- 
doderm,  having  the  same 
general  relations  as  in  the 
body  of  the  hydra.  These 
are  the  primary  germ  layers. 
Here  they  are  not  obviously 
differentiated  at  first  except 
by  their  position.  This  form 
of  embryonic  body  is  called  a 
gastrula,  and  the  process  of 
invagination  by  which  it  is 
produced  is  called  gastrula- 
Uon.  The  cavity  which  cor- 
responds to  the  food  cavity 
of  the  hydra  is  called  the 
arch-enter  on. 

A   third   germ   layer,   the 
mesoderm,    appears    in    the 

Fig.      108.      Diagrams    illustrating  fur-  1      c                           1     ,  • 

ther     development     of      the      earth  WOrm    beiOrC    gaStrulatlOn    IS 

worm,      a  and  6,  longitudinal  sections  1-1          t,          •     •        , 

of  later  stages;  c,  d  and  e,  cross  sec-  Completed.        it  Originates   aS 

tions     of      the    loody     showing    the  .                  , ,         ^        n      •     j       j  1 

splitting  of    the    mesoderm    and   the  an  lUgrOWth  OI  CCllS  lUtO  the 

formation  of  the  ventral  nerve  cord.  ,      ,  . 

The  ectoderm  is  white,    the  endo-    narrow  Segmentation  cavity, 

derm  is  crosslmed  and  the  mesoderm  •      1  •       j      1     •        ,^ 

is  hatcheled.n,  nerve  cord.  aS    mdlCated    lU    thC    aCCOm- 

panying  diagrams.  The 
diagrams  of  figure  io8  show  also  how  it  splits  into  two  layers 
(joined  by  rows  of  cells  that  later  develop  into  the  septa)  the 


172  GENERAL  BIOLOGY 

inner  one  of  which  (the  splanchnic  layer)  becomes  applied 
against  the  endoderm  to  form  the  larger  part  of  the  wall  of 
the  enteron;  the  other  (the  somatic  layer),  applied 
to  the  ectoderm,  becomes  much  the  greater  part  of  the  body 
wall.  The  cleft  between  these  layers  is  the  coelom.  The 
blastopore  in  the  worm  becomes  the  mouth;  the  breaking 
through  of  the  tissues  at  the  opposite  end  of  the  body 
transforms  the  primitive  food  sac  into  an  alimentary 
canal — having  the  obvious  advantage  of  permitting  unin- 
terrupted passage  of  food, and  facilitating  also  the  struc-' 
tural  and  physiological  differentiation  of  parts  along  the  way. 
Thus  at  a  very  early  stage  of  its  development,  the  fun- 
damentals of  the  plan  of  structure  of  the  earthworm  are 
clearly  established. 

Later  development. — After  the  completion  of  the  enter- 
on,  there  occurs  along  with  the  rapid  elongation  of  the 
body,  an  ingrowth  of  the  ectoderm  at  both  ends  (but 
principally  at  the  front  end)  which  results  in  the  restriction 
of  the  endoderm  to  that  part  already  designated  in  the 
adult  worm  as  stomach-intestine.  The  diagram  of  figure 
lo^d  indicates  roughly  the  distribution  the  three  germ 
layers  acquire. 

The  three  are  unlike  in  the  nature  and  extent  of  the 
differentiation  of  their  cells  in  the  formation  of  tissues.  The 
embryonic  endoderm  becomes  the  adult  epithelium — diges- 
tive epithelium  (and  that  only)  in  the  worm.  The  ectoderm 
differentiates  chiefly  into  two  sorts  of  cells:  i)  into  epider- 
mis, which  remains  in  the  original  position  on  the  surface 
of  the  body  and  fulfills  the  primitive  function  of  protection ; 
and  2)  nerve  cells,  which  are  separated  off  from  the  ectoderm 
upon  the  ventral  side  as  indicated  in  figure  loSc,  d,e,  and 
pass  between  the  developing  masses  of  mesoderm  to  lie 
within  the  coelom  and  to  develop  there  the  nervous  tissue 
(covered,  however,  by  an  investment  that  is  of  mesodermal 
origin) . 


ORGANIC  EVOLUTION 


173 


m 


These  nerve  cells  cease  early  to  divide  and  develop 
among  themselves  intercommunicating  processes,  and 
externally,  other  longer  and  slenderer  unbranched  processes 
which  become  the  nerve  fibres,  and  extend  to  remote  parts 

of  the  body.  The  orig- 
inal cell  heaps  become 
the  ganglia  which  col- 
lectively make  up  the 
cord,  and  each  ganglion 
becomes  the  centre  for 
the  receipt  of  stimuli 
and  coordination  of  re- 
sponses for  all  the  parts 
of  its  segment.  These 
cells  have  no  other  func- 
tion than  sensory  com- 
munication between  the 
parts  of  the  body:  the 
accompanying  diagram 
(fig.  109)  shows  an  ar- 
rangement clearly  adap- 
ted to  that  office. 

Mesoderm  we  did  not 
find  in  the  hydra,  but  in 
the  worm  it  gives  rise  to 
the  greater  part  of  the 
adult  body.  The  germ 
cells  remain  in  the 
mesoderm  unspecialized. 
The  leucocytes,  (or 
white  "corpuscles")  of  the  blood,  also,  retain  a  singularly 
primitive  amoeboid  form.  They  move  about  freely  in 
the  fluids  of  the  coelom,  where  they  serve  the  useful 
function  of  feeding  on  bacteria  and  other  foreign  substances 


n 


Fig.  109.  Diagram  of  distribution  of  nerve 
cells  and  fibres  m  the  portion  of  the  ventral 
nerve  cord  of  the  worm  lying  in  two  seg- 
ments (m  and  n) ;  cell  a  sends  fibres  forward 
and  backward  within  the  cord ;  e  and  /,  are 
centrally  located  multipolar  cells;  all  the 
others  are  uninipolar;  b,  sends  a  fibre  out 
on  its  own  side;  candd,  each  sends  a  fibre 
out  too  through  a  nerve  on  the  opposite  side 
of  the  cord  (after  Retzius). 


174 


GENERAL  BIOLOGY 


and  carrying  them  out  through  the  tissues  of  the  body  wall 
to  the  surface  and  thus,  removing  them.  The  nephridia 
develop  from  the  mesoderm,  also,  but  the  greater  part  of 
the  mesodermal  cells  develop  into  muscle  fibres.  They 
elongate  greatly,  and  acquire  a  structure  especially  fitting 


KARL    ERNST    VON    BAER 

(1792-1876) 

The  founder  of  comparative  embryology. 

them  for  contracting  in  one  direction.  The  tissue  that  over- 
spreads the  walls  of  the  coelorn.  (formed,  as  already  seen,  by 
the  splitting  of  the  mesoderm)  is  the  peritoneum.  It  con- 
sists for  the  most  part  of  thin  flat  covering  cells,  but 
where  these  cells  overlie  the  stomach-intestine  they  become 
distended  with  waste  assimilation  products  and  take  on  an 


ORGANIC  EVOLUTION  175 

inverted  flask-shaped  form,  and  are  then   known  as   chlora- 
gogue  cells. 

These  are  but  the  barest  outlines  of  the  principal  develop- 
mental processes.  We  have  not  time  to  enter  farther  into 
the  field  of  embryology.  We  have  gone  far  enough  to  see 
that  the  development  of  an  organism  from  an  egg  is  a  truly 
wonderful  process.  We  need  but  go  back  again  and  look  at 
the  marvelous  simplicity  of  the  egg  to  be  convinced  of  it. 
Not  only  do  cells  differentiate,  but  cell  groups  act  together 
like  well  drilled  battalions,  cleaving  apart  here,  fusing 
together  there,  forming  protective  coverings  or  communicat- 
ing channels,  apparently  creating  out  of  nothing,  a  whole 
set  of  nutritive  and  reproductive  organs,  all  in  orderly  and 
progressive  sequence,  producing  in  the  end  that  orderly  dis- 
posed cell  aggregate,  that  individual  life  unit,  which  we 
know  as  an  earthworm.  Although  the  forces  involved  are 
beyond  our  ken,  the  grosser  processes  are  evident,  and  may 
be  summarized  as  follows : 

1.  In  respect  to  development,  the  general  phenomena 
are :    cell  multiplication  and  cell  differentiation. 

2.  The  principal  changes  of  form  and  relations  are: 
segmentation,  gastrulation,  formation  of  the  mesoderm, 
splitting  of  the  mesoderm,  formation  of  the  anus,  origin  of 
the  nervous  system  from  the  ectoderm,  origin  of  the  nephri- 
dia  and  reproductive  organs  from  the  mesoderm,  ingrowth 
of  the  ectoderm  to  form  stomodaeum  and  proctodeum. 
These  are  the  A,  B,  C's  of  embryology. 

3.  The  derivation  of  the  principal  tissues  from  the  three 
germ  layers  is:     From  the  ectoderm: 

epidermis  and  setae 

lining  of  stomodaeum  and  proctodeum 

the  whole  nervous  system. 
From  the  endoderm:  the  alimentary  epithelium 
From  the  mesoderm : 


176  GEXERAL  BIOLOGY 

muscle  and  connective  tissue 

blood  and  blood  vessels 

peritoneum  and  chloragogue 

nephridia 

reproductive  organs 
Let  us  now  try  to  get  a  bird's  eye  view  of  the  life  process 
in  the  worm.  Both  the  substance  for  the  building  of  its 
body  and  the  energy  for  its  operation  are  contained  in  the 
food.  This  consists  of  organic  matter  (proteins  and  carbo- 
hydrates) and  salt  solutions  mixed  with  a  remarkable  large 
proportion  of  indigestible  materials  (sand,  clay,  etc.),  in  the 
earth  and  rubbish  that  the  worm  swallows :  also,  of  the  free 
oxygen  absorbed  through  the  skin  from  the  air.  The  solid 
food  is  pulled  to  pieces  by  the  prostomium,  sucked  in  by  the 
pharynx,  passed  down  the  slender  esophagus  to  a 
temporary  storage  in  the  crop  and  triturated  by  the  gizzard 
(all  purely  mechanical  treatment),  perhaps  mixed  with 
some  secretions  along  the  way,  and  then  passed  on  into  the 
stomach-intestine.  Here  digestion  and  absorption  take 
place.  These  are  the  work  of  the  epithelial  cells.  But 
these  cells  are  remote  from  many  parts  of  the  body,  and  all 
parts  have  to  be  fed,  therefore,  the  food  must  be  trans- 
ported. Circulatory  apparatus  exists  because  the  slow 
process  of  diffusion  is  inadequate  to  the  needs  of  so  large  and 
active  an  organism.  Into  the  blood  percolating  through 
the  intercellular  spaces  about  the  bases  of  the  epithelial  cells 
the  dissolved  food  diffuses,  and  passes  upward  through  the 
dorso-intestinal  vessels  to  enter  the  great  dorsal  trunk  for 
distribution  all  over  the  body  to  every  living  cell. 

For  nutrition  is  at  bottom  the  work  of  the  cell.  One  set 
of  cells  may  attend  to  the  digesting  and  another  to  the  cir- 
culating of  the  digested  material,  but  every  cell  must  eat  for 
itself.  No  amount  of  division  of  labor  can  relieve  any  cell 
of  the  necessity  of  assimilating  and  excreting.     For  these 


ORGANIC   EVOLUTION  177 

metabolic  processes  oxygen  is  also  necessary,  and  this  the 
worm  gets  after  a  very  primitive  fashion — by  direct  absorp- 
tion through  the  skin.  To  facilitate  this  the  skin  is  kept 
moistened  with  the  watery  mucous  poured  out  upon  it  by 
numerous  secreting  cells  in  the  epidermis  (fig.  104  b,  h). 

The  red  color  of  the  blood  is  due  to  the  presence  in  it  of 
haemoglobin,  a  substance  that  is  an  excellent  agent  for  the 
transport  of  oxygen.  It  combines  loosely  with  free  oxygen, 
taking  it  up  readily  where  there  is  a  copious  supply,  as  at 
the  skin,  and  giving  it  up  easily,  where  affinities  for  it  are 
stronger,  as  in  the  active  and  deoxydized  tissues.  The  blood 
is,  therefore,  the  carrier  of  both  food  and  oxygen  to  every  cell. 
It  carries  the  former  outward  from  the  stomach  wall,  the 
latter  inward  from  the  skin. 

Income  and  outgo  are  not  essentially  different  for  any  cell 
in  the  worm's  body  from  the  same  process  in  the  protozoan 
cell  as  outlined  on  p.  91.  More  food  passes  through  the 
epithelial  cell  and  more  oxygen  through  the  epidermal  cell 
than  through  the  others,  as  more  stores  pass  through  the 
seaport  towns  of  an  importing  country  than  through  the 
interior  ones ;  but  the  part  reserved  by  each  for  its  own  use 
is  used  by  all  in  much  the  same  way.  The  output  of  matter 
is  therefore,  as  in  the  protozoan,  mainly  water,  carbonic  acid 
gas  and  simple  nitrogen  compounds. 

These  waste  products  must  be  gotten  rid  of,  and  while 
the  cellsof  the  surfaces  of  the  body  may  excrete  them  direc  tly 
to  the  outside,  those  of  the  interior  need  the  circulatory 
system  to  carry  off  their  waste.  The  dispersal  of  the  carbon 
dioxide  and  water  is  as  general  over  the  surface  of  the  body 
as  the  intake  of  oxygen.  With  these  doubtless  goes  a  part 
of  the  nitrogen  waste  also.  But  the  nephridia  are  special 
agents  for  disposal  of  the  nitrogen  waste.  To  these  the 
blood  goes,  laden  with  the  products  of  proteid  dissimilation, 
and  in  them  these  substance  are  removed  and  passed  to  the 
exterior. 


178  GENERAL  BIOLOGY 

Another  and  very  peculiar  mode  of  waste  disposal  occurs 
in  the  worm.  The  cells  of  the  peritoneum,  where  they  cover 
the  parts  chiefly  concerned  with  the  elaboration  of  the  food, 
(stomach-intestine  and  larger  blood  vessels  leading  forward 
therefrom)  instead  of  remaining  thin  and  flat  become  elevated 
into  high  pear-shaped  sac-like  bodies  attached  by  their 
slender  pointed  ends,  and  filled  more  or  less  completely  with 
yellowish-green  granules  of  a  substance  called  chloragogue. 
It  is  not  quite  certain  w^hat  is  the  nature  of  these  granules 
but  they  are  believed  to  be  waste  nitrogenous  products, 
and  it  is  certain  that  they  accumulate  in  the  cells  until  the 
cells  are  distended  and  burst.  Then  they  fall  free  into  the 
body  cavity.  A  drop  of  the  body  fluid  taken  at  random 
with  a  pipette  from,  an  adult  worm  is  certain  to  contain  num- 
bers of  these  isolated  greenish-yellow  granules.  They  filter 
posteriorly  through  the  holes  in  the  septa,  and  finally  accu- 
mulate in  little  brownish  lumps,  intermixed  with  dislodged 
setae,  in  a  few  of  the  hindmost  segments.  There  they 
are  consumed  by  commensal  nematodes.  The  blood  always 
contains,  besides  these  granules  and  leucocytes  already  men- 
tioned, great  numbers  of  bacteria,  which  the  latter  feed 
upon,  and  occasional  parasites. 

Study  24.     The  general  structure  of  the  earthworm. 

Materials  needed :  Live  worms  of  large  size ;  specimens 
well  preserved  and  hardened :  small  dissecting  trays  and  tools. 

Study  the  live  worm,  its  movements,  its  sensibility  to 
touch,  the  way  it  uses  its  set«.  Turn  it  over  and  watch  it 
right  itself.     Note  all  external  features. 

In  a  freshly  opened  worm  make  a  general  survey  of  the 
internal  organs,  guided  by  the  description  of  the  preceding 
pages  in  the  following  order:  alimentary  canal,  circulatory 
system,  nervous  system,  reproductive  organs,  excretory 
organs.     Then  remove  these  organs  and  observe  in  the  body 


ORGANIC  EVOLUTION  179 

wall  the  distribution  of  muscle  bands  and  the  location  of  the 
rows  of  setae. 

The  records  of  this  study  may  consist  in  a  carefully  pre- 
pared diagram  to  show  the  relation  of  the  organs  (except 
reproductive  and  excretory)  in  the  median  plane  of  the 
body.  Also,  a  tabular  statement  of  the  parts  that  are 
repeated  in  each  segment:     a)  organs;   b)  parts  of  organs. 

Study  25.      The  cellular  structure  of  the  earthworm. 

Materials  needed:  Live  worms  and  prepared  slides  of 
cross  sections. 

Examine  the  blood  of  the  worm  (taken  with  a  pipette 
from  the  coelom  of  an  anesthetized  specimen)  for  leucoc}^es, 
bacteria,  loose  chloragogue  granules,  etc. 

Examine  a  drop  of  the  fluid  from  the  sperm  vesicles  for 
sperm  cells  in  clusters  in  various  stages  of  development. 

Examine  a  mounted  ovary,  either  fresh  or  a  stained 
preparation. 

Study  cross  sections  of  the  worm's  body  and  identify 
all  the  tissue  composing  it. 

The  record  for  this  work  may  consist  in  drawings  of  leuco- 
cytes, sperm  cells,  egg  cells  in  the  ovary,  and  a  few  typical 
cells  from  the  more  important  tissues  of  the  body,  such  as 
epithelium  and  hypodermis.  Also  a  tabular  statement 
of  the  spatial  relations  of  the  tissues  passing  from  the 
outside  inward  in:     a)  body  wall,  and  b)  enteron  wall. 

THE    SALAMANDER. 

The  spotted  salamander  {Amby stoma  tigrinum)  is  a  very 
common  vertebrate,  of  rather  primitive  structure.  It  will 
serve  very  well  to  illustrate  that  type  of  animal  organization 
that  is  found  in  our  own  bodies.  It  is  nocturnal  and  very 
secretive  in  its  habits,  being  often  seen  in  cellars  and  base- 
ments, although  occasionally  dug  up  in  moist  garden  soil, 


t8o  ■  GENERAL  BIOLOGY 

or  found  by  overturning  logs,  etc.,  in  the  woods.  It  is  of 
elongate  form  (fig.  no),  with  a  moist  scaleless  skin,  short 
legs,  that  are  used  more  for  propulsion  than  for  support,  and 
with  a  stout  laterally  flattened  tail.  It  is  of  greenish-black 
color,  ornamented  with  irregular  and  variable  yellow  spots. 
Its  appearance  excites  the  fears  of  some  superstitious  and 
ignorant  people,  but  it  is  quite  harmless  and  inoffensive. 

Specimens  are  easiest  obtained  by  taking  advantage  of 
their  mishaps.  They  migrate  from  the  fields  and  woods 
back  toward  their  native  ponds  in  late  fall  and  early  spring, 
and  fall  into  any  hole  that  lies  in  their  path.     In  crawling 


Fig.  110.     The  spotted  salamander,  Ambystoma  tigrinum. 

about  the  foundations  of  buildings  they  get  into  basements; 
the  walled  semicircular  pits  surrounding  old-fashioned  base- 
ment windows  capture  many  of  them.  They  will  fall  into 
any  hole  that  offers,  but  can  crawl  out  again  if  the  sides  be 
not  rather  smooth  and  vertical.  Any  low  barrier  interposed 
between  a  pond  and  adjacent  hills,  such  as  a  long  curbing  or 
a  railroad  track  if  the  rail  rest  continuously  on  the  ground, 
will  detain  them  temporarily,  where  they  can  be  picked  up 
with  the  aid  of  a  lantern  at  night.  They  are  easily  kept  in 
any  cool  moist  place  and  need  no  food  in  winter. 

If  a  living  salamander  be  examined  some  of  the  characters 
of  back  boned  animals  will  be  readily  apparent.  First  of  all, 
the  axis  of  support  (fig.  in,  spinal  column  composed  of 
vertebrae)   is  located  in  the  body  wall  upon  the  dorsal  side 


ORGANIC   EVOLUTION 


i8l 


X 


\y< 


y 


V  \  M 


^  ,..v 


III, 


1 1 1/ 


and  in  consequence  the  thick 
dorsal  wall  of  the  body  stands 
in  marked  contrast  with  the 
thin  and  soft  ventral  wall. 
This  axis  is  extended  posterior- 
ly into  the  tail,  and  expanded 
anteriorly  to  form  part  of  the 
skull,  which  is  the  skeleton  of 
the  head,  and  which  may 
readily  be  felt  with  the  fingers 
through  the  soft  skin.  Two 
pairs  of  appendages  are  quite 
characteristic  of  vertebrates. 
The  close  correspondence  be- 
tween fore  and  hind  limb  will 
be  obvious  even  in  the  living 
specimen.  Both  have  a  sup- 
porting girdle  of  bone  embed- 
ded in  the  side  walls  of  the 
body  and  more  or  less  firmly 
attached  to  the  axial  skeleton. 
Upper  arm,  fore  arm,  wTist  and  hand,  in  the  fore  limb, 
correspond  to  thigh,  shank,  ankle  and  foot,  respectively,  of 
the  hind  limb.  The  divisions  betAveen  these  joints  may 
readily  be  determined  by  flexing  them  between  the  fingers. 
Were  not  this  internal  jointed  skeleton,  with  its  numerous 
bones  united  by  strong  ligaments  and  moved  upon  each 
other  by  the  over  lying  muscles  so  familiar  to  us,  its 
mechanical  fitness  would  be  most  impressive. 

Another  small  part  of  the  skeleton,  located  in  the  ventral 
wall  in  the  region  of  the  throat,  is  the  hyoid  apparatus  (fig. 
112).  This  is  mainly  cartilaginous,  only  the  part  that  is 
stippled  in  the  figure  being  bony.  The  anterior  fork  sup- 
ports the  base  of  the  tongue ;  the  postero-lateral  arms  curve 


I 
I 

r 


Fig.  111.  Diagram  of  a  vertebrate 
skeleton,  x,  skull;  y,  fore  limb; 
z,  hind  limb;  /,  2,  j,  in  front, 
clavicle,  coracoid,  and  scap- 
ula, composing  the  shoulder 
girdle;  /,  2,  j,  behind,  ilium,  is- 
chium and  pubis,  composing  the 
hip  girdle. 


l82 


GENERAL  BIOLOGY 


upward  about  the  sides  of  the  neck.    These  maybe  felt  with 

the    fingers    beneath 
the  skin  of  the  throat, 
or  moved  about  under 
the    skin   by   moving 
the  tongue  with  a  for- 
ceps.    This    part    of 
the    skeleton,  though 
small  and  weak,  is  of 
great    historical    im- 
portance. These 
paired     cartilaginous 
arches  are  landmarks 
of  vertebrate  history: 
to       their        consid- 
eration      we       shall 
have  occasion  to  re- 
turn later. 

The  eyes  of  the  salamander  are  prominent  and  shining 
and  they  both  wink  at  once  at  long  intervals.  If  one  of  them 
be  touched  gently,  it  will  be  withdrawn  completely  into  its 
orbital  cavity;     thus  it  gets  out  of  harm's  way. 

Once  in  a  while  the  salamander  may  be  seen  to  gulp 
down  a  mouthful  of  air.  It  does  not  inhale;  to  get  air 
down  it  has  to  swallow.  The  air-swallowing  process  will 
often  be  most  clearly  seen  after  the  specimen  has  been 
handled  and  put  down  again.  On  the  under  side  of  the 
neck  the  pulse  beat  may  be  seen. 

On  the  body  there  is  a  mid-dorsal  groove  extending  from 
the  rear  of  the  head  to  the  base  of  the  tail,  and  there  is  a 
series  of  costal  grooves  between  fore  and  hind  legs  traversing 
the  sides  of  the  body  vertically.  These  latter  are  the  exter- 
nal evidence  of  that  segmentation  of  the  body  that  will  be 
found  later  in  the  vertebrae,  spinal  nerves  and  ganglia,  and 


Fig  112.  The  branchial  skeleton  from  the  throat 
of'  the  salamander,  /i,  the  hyoid  arch;  /  and  2, 
latet  al  arms  of  the  first  and  second  branchial 
arches;  i,  isolated  basal  piece  corresponding  to 
the  missing  branchial  arches. 


ORGANIC    EVOLUTION  183 

muscle  segments.  A  number  of  similar  grooves  may  be 
seen  on  the  sides  of  the  tail,  especially  at  its  base.  The 
surface  of  the  skin  is  covered  with  the  very  minute  openings 
of  pores  from  the  large  skin  glands  within  it.  These  pores 
are  visible  with  a  lens.  These  glands  pour  out  the  secretion 
which  keeps  the  skin  moist  and  enables  the  salamander  to 
get  its  oxygen,  as  the  worm  does,  in  a  large  part  by  direct 
absorption .  It  depends  far  less  on  its  lungs  for  air  than 
do  the  higher  vertebrates.  Some  vestiges  of  its  early 
aquatic  life  are  preserved  in  the  rudimentary  webbing 
between  the  bases  of  the  toes,  and  in  the  flattening  of  the 
tail,  which  is  still  put  through  superfluous  sculling  motions 
when  the  salamander  tries  to  run  on  land. 

At  the  tip  of  the  snout  a  pair  of  small  nostrils  will  be  seen, 
each  with  a  blackish  valve-like  flap  attached  to  its  hind 
margin  within,  and  if  the  mouth  be  held  open  widely,  the  in- 
ner openings  from  these  nostrils  may  be  seen  on  its  roof  at 
the  rear  of  the  palate.  On  the  floor  of  the  mouth  lies  a  fleshy 
tongue,  attached  along  its  middle  line,  its  edges  lying  free; 
at  the  rear  of  the  mouth,  the  pharynx,  with  its  walls  con- 
verging to  the  esophagus,  penetrated  by  abundant  minute 
blood  vessels,  which  give  to  it  something  of  the  character  of 
a  respiratory  organ.  In  the  lungless  salamanders  this 
organ  is  better  developed  to  serve  that  function.  On  the 
floor  of  the  pharynx  is  the  glottis,  the  gateway  to  the  lungs, 
a  narrow  longitudinal  slit  with  closely  appressed  cartilagi- 
nous lips.  Very  minute  and  numerous  teeth  may  be  found 
on  the  edges  of  the  jaw  by  scraping  it  with  a  finger-nail  or 
with  a  needle,  and  two  patches  of  palatine  teeth  may  be 
found  farther  back  in  the  roof  of  the  mouth. 

Internal  features. — Upon  looking  inside  the  body  of  the 
salamander  it  is  at  once  apparent  that  the  main  general 
features  of  structure  that  were  found  to  characterize  the 
earthworm,    are    repeated    here.     There    is    a    compound- 


i84 


GENERAL   BIOLOGY 


tubular  body,  a  tube  within  a  tube,  and  a  coelom  or  body 
cavity  between ;  the  inner  tube  is  the  alimentary  canal  and 
the  outer  one  is  the  body  wall  as  before,  but  the  alimen- 
tary canal  differs  in  tw^o  important  particulars;  it  is  not 
straight,  but  greatly  coiled  and  twisted;  and  it  is  not  simple, 
but  bears  conspicuous  appendages.  And  the  body  wall 
differs  conspicuously  in  that  it  bears  a  differentiated  head, 
and  is  extended  laterally  into  limbs  and  backw^ard  into  a 

tail. 

On  comparing  the  internal  organs  there  are  strong  con- 
trasts.    The  central  part  of  the  circulatory  system  is  not  a 


a  ^ 

Fig.  113.  Diagrams  illustrating  the  plan  of  body  in  worm 
and  in  salamander  {b)  in  cross  section;  c,  enteron;  c, 
coelom ;  n,  central  nervous  apparatus ;  v,  central  circula- 
tory apparatus. 

long  pulsating  tube  lying  on  the  dorsal  side,  but  a  heart, 
lying  upon  the  ventral  side.  The  central  part  of  the  ner- 
vous system  does  not  lie  within  the  coelom  on  the  ventral 
side,  but  in  the  body  wall  upon  the  dorsal  side.  The 
nephridia  are  not  scattered  segmentally  in  single  pairs  the 
whole  length  of  the  body,  but  are  aggregated  into  special 
paired  organs,  the  kidneys,  and  in  the  salamander  there  are 
special  respiratory  organs  the  lungs,  and  special  supporting 
structures,  the  bones. 
The  food  tube,  alimentary  canal,  or  enteron,  is  differentiated 
into  parts  the  anterior  of  which  bear  the  same  names  as 
parts  of  like  function  in  the  earth  worm:     mouth,  pharynx 


ORGANIC   EVOLUTION  185 

and  esophagus,  and  these  are  succeeded  by  stomach, 
small  intestine,  large  intestine  and  cloaca.  All  these, 
together  with  the  appendages,  are  indicated  in  the  accom- 
panying diagram  (fig.  114).  Such  differentiation  of  parts 
bespeaks  many  separate  localized  functions  along  the  course 
of  the  enteron ;  and  such  indeed  there  are,  but  we  are  here 
concerned  with  form  changes  and  can  note  only  the  more 
important  functions  as  bound  up  with  the  principal  organs. 
The  stomach  has  become  a  sharply  delimited  organ  for 
the  reception  of  food,  capacious,  distensible,  suited  to  the 
exigencies  of  irregular  food  supply.  Its  thick  muscular 
walls  are  filled  with  small  gastric  glands,  whose  secretion 
initiates  digestion.     The  churning  movements  of  the  walls 


Fig.  1 14.  Diagram  of  the  enteron  of  the  salamander,  with 
its  principal  appendages,  o,  mouth:  /,  pharynx;  e,  eso- 
phagus; d,  stomach;  i,  small  intestine;  /  large  intes- 
tine; c.cloaca;  a,  anus; &,  urinary  bladder;  g,  gall  bladder 
on  w,  liver;  w,  pancreas;  /,  lung. 

aid  in  the  comminution  of  the  food  and  in  the  mixing  of  it 
with  the  gastric  secretion.  At  the  outlet  of  the  stomach  is 
a  guarded  passageway  called  the  pylorus,  through  which  the 
food  passes,  when  reduced  to  a  more  or  less  fluid  condition. 
The  small  intestine  is  a  narrow  passageway  (greatly 
abbreviated  in  the  diagram) ,  well  adapted  to  the  slow  pas- 
sage of  the  food,  to  the  completion  of  its  digestion,  and  to  the 
extraction  from  it  of  assimilable  materials.  It  is  long  and 
tortuous.  Its  walls  are  covered  internally  with  folds  and 
processes  {villi)  which  greatly  increase  the  surface  in  con- 
tact with  the  passing  stream.  These  secure  the  better  mix- 
ing of  food  with  the  digestive  secretions  of  the  liver  and  the 
pancreas,  and  the  completer  absorption  of  it  after  digestion. 


i86  GENERAL   BIOLOGY 

The  principal  appendages  of  the  enteron. — The  lung  is 
here  a  new  feature.  As  a  respiratory  sac  appended  to  the 
alimentary  canal,  it  is  peculiar  to  vertebrates.  Among 
terrestrial  animals,  most  vertebrates  are  giants,  for  whom 
direct  absorption  of  oxygen  through  the  skin  would  be  quite 
inadequate.  Herein  is  seen  the  advantage  of  the  lung, 
which  maintains  inside  the  body  extensive  surfaces  that  are 
thin-skinned  and  always  moist. 

The  liver  is  the  largest  gland  in  the  body,  a  lobed  organ  of 
mottled  brownish  color,  its  pointed  left  lobe  partially  cover- 
ing the  stomach  (in  the  resupinated  position  in  which  the 
salamander  is  opened) .  Its  secretion  is  collected  in  a  bluish- 
green  sac — the  gall  cyst,  which  the  right  lobe  overlies.  The 
cyst  is  connected  by  a  slender  bile  duct  with  the  small 
intestine  near  the  stomach.  Compression  upon  the  gall 
cyst  will  usually  demonstrate  that  the  bile  duct  opens  at 
this  point,  by  driving  the  greenish  bile  down  its  length,  mak- 
ing the  duct  visible.  The  pancreas  is  an  elongated  thin  flat 
fatty-looking  organ,  that  lies  in  the  loop  formed  by  the 
junction  of  the  stomach  and  small  intestine  and  is  covered 
by  the  liver  except  at  its  posterior  end  where  it  touches  the 
intestine.  The  urinary  bladder  is  the  hindmost  appendage 
of  the  alimentary  canal.  It  is  a  thin,  crumpled  sac  that  lies 
upon  the  ventral  surface  of  the  large  intestine,  and  opens 
into  the  cloaca.  Its  connection  with  the  excretory  system 
will  be  discussed  later.  The  thin  sheet  of  membrane  in 
which  these  digestive  organs  are  slung  from  the  dorsal  side 
of  the  body  wall  a.nd  through  which  pass  numerous  branch- 
ing incoming  and  outgoing  blood  vessels,  is  the  mesentery. 
The  elongate  oval  reddish  body  suspended  in  the  mesen- 
tery behind  the  stomach  is  the  spleen. 

The  lungs  are  the  foremost  appendages  of  the  alimentary 
canal.  They  spring  from  the  ventral  side  of  the  pharynx 
at  the  glottis,  whose    location    has    already    been  noted, 


ORGANIC  EVOLUTION 


187 


by  a  slender  hollow  stalk-like  trachea,  which  divides  into 
two  bronchial  tubes,  joining  the  right  and  left  lungs. 
By  passing  a  pointed  glass  tube  into  the  glottis  and  inflating 
the  lungs,  their  size,  their  constituent  air  cells  and  the  com- 
municating blood  vessels  in  their  wall  may  be  clearly  seen. 
The  circulatory  system  has  for  its  central  organ  a  heart  of 

three  chambers,  two  aur- 
icles and  a  ventricle  (fig. 
115).  The  ventricle  has 
thick  muscular  walls,  and 
is  the  chief  propelling 
agent  of  the  blood  cur- 
rent. It  drives  the  blood 
forward  through  the  ar- 
terial trunk,  and  out- 
ward through  the  arches, 
as  indicated  in  the  ac- 
companying diagram. 
The  outward  current  is 
called  the  arterial,  the  in- 
ward, the  venous  circula- 
tion. 

The  carotid  arch  carries 
blood  anteriorly  to  the 
head,  the  pulmo-cutan- 
eous  inwardly  to  the  lungs  and  externally  to  the  skin 
(whence  its  name),  and  the  aortic  arch  carries  the 
greatest  supply  posteriorly  and  to  peripheral  parts  of  the 
body,  and  distributes  vessels  through  the  mesentery  to  the 
internal  organs. 

The  return  currents  reach  the  heart  separately,  entering 
by  the  two  auricles.  That  entering  the  left  auricle  is 
returned  from  the  lungs  through  the  pulmonary  veins. 
That  entering  the  right  auricle  (by  way  of  the  venous  sinus,  a 


Fig.  1 15.  Diagram  of  the  Amphibian  heart, 
and  principal  blood  vessels.  a,  right 
auricle;  b,  left  auricle;  c,  ventricle;  t, 
arterial  trunk;  e,  lung;  d,  liver;  /,  carotid 
arch;  g,  aortic  arch;  h,  pulmo-cutaneous 
arch,  with  -i,  its  cutaneous,  and  j,  its  pul- 
monary branch;  k,  pulmonary  vein,  with 
the  base  of  the  corresponding  vein  from 
the  missing  lung  shown  at  /,  m,  the  right 
precaval  vem;  n,  postcava;  o,  anterior 
abdominal  vein  and  p,  portal  vein. 


i88  GENERAL  BIOLOGY 

vestibule  attached  to  the  auricle)  is  returned  from  the  front 
by  the  precava,  and  from  the  rear  by  the  postcava.  The 
postcava  is  the  largest  bloodvessel  coming  from  the  rear. 
Into  the  liver  the  blood  returns  by  two  main  channels,  an 
anterior  abdominal  vein  that  traverses  the  mid-ventral  line 
of  the  body  wall  and  jumps  across  the  short  intervening 
space  of  the  coelom  to  enter  the  liver  on  its  ventral  side,  and 
a  portal  vein  that  comes  from  the  stomach  and  succeeding 
portions  of  the  alimentary  canal. 

The  special  organs  of  excretion  in  the  salamander  are  the 
kidneys,  a  pair  of  chocolate-colored  bodies  lying  closely 
applied  to  the  dorsal  wall  in  the  posterior  end  of  the  body 
cavity,  broader  and  thicker  behind,  and  tapering  to  a 
slender  point  in  front.  From  their  postero-extemal  angles 
a  pair  of  very  short  ducts  connects  with  the  cloaca,  entering 
just  opposite  the  mouth  of  the  urinary  bladder,  into  which 
the  discharge  of  their  urine  passes  for  temporary  storage. 
A  large  vein  enters  each  kidney  from  the  rear,  breaks  up  into 
fine  branchlets,  and  is  reformed  on  the  opposite  internal 
side,  where,  by  confluence  of  emerging  branchlets,  the 
postcava  is  formed. 

The  reproductive  organs  lie  in  the  midst  of  the  body 
cavity,  a  single  pair  just  ventral  to  the  pointed  anterior  ends 
of  the  kidneys,  and  they  bear  usually  a  considerable 
development  of  fat  in  the  form  of  yellowish  finger-like 
processes  (fig.  ii6.).  The  salamander  being  unisexual, 
they  are  spermaries  {testes)  in  the  male  and  ovaries 
in  the  female.  The  spermaries  are  oval  yellowish 
bodies,  which  discharge  their  sperms  through  a  number 
of  fine  ducts  that  penetrate  the  substance  of  the  kidney 
and  emerge  on  the  opposite  side  to  join  the  ureter,  and 
thence  reach  the  cloaca.  The  ovaries  are  large  mem- 
branous, crumpled  organs  in  whose  walls  the  eggs  may  be 
seen  developing,   opaque    and   white     at    first,    acquiring 


¥^ 


ORGANIC  EVOLUTION 


189 


Fig.  116.  Diagram  of  the 
relations  of  renal  and  repro- 
ductive organs  in  amphi- 
bians, male  above,  female 
below,  k,  k,  kidneys;  u,  u, 
ureters;  cl,  cloaca;  5,  5,  sper- 
maries  (testes).  Arrows  in- 
dicate the  course  of  the 
sperm  ducts  through  the 
kidneys  to  join  the  ureter; 
a,  a,  fat  body;  o,  o,  ovaries; 
d,  d,  oviducts;  /,  /,  their 
funnel  shaped  openings  into 
the  ccelom;  t,  t,  the  dilata- 
tion(uterus)  at  the  lower  end 
of  each. 


blackish  pigment  as  they  increase  in  size,  studding  the 
transparent  membrane.  The  eggs  are  shed  from  the 
ovaries  into  the  body  cavity  and  the  ducts  by  which  they 
reach  the  exterior  are  not  connected  to  the  ovaries  at  all. 
The  oviducts  are  long  sinuous  tubules  extending  the  whole 
length  of  the  body  cavity  near  the  mid-dorsal  line,  opening 

by  a    V-shaped 
slit    at   the   an- 
terior end   that 
is  situated     be- 
tween the  esoph- 
agus    and     the 
shoulder,    and 
into    which  the 
eggs   find    their 
way,    aided    by 
J     the  lining  cilia.     As  the  eggs  pass  down 
the  tube  a  gelatinous  secretion  is  added 
to  them  by  cells    along   the    way,     and 
d    they  find  temporary  storage   in  a  sac- 
culation (uterus)  at  the  lower  end  of  the 
duct  just  before  it  enters  the  cloaca. 

Nervous  system. — As  already  noted, 
the  central  part  of  the  nervous  system 
in  the  salamander,  as  in  vertebrates 
generally,  is  lodged  in  the  body  wall 
upon  the  dorsal  side.  It  consists  of  a 
hollow,  but  thick  walled  tube  of  nervous 
matter,  differentiated  into  two  principal  parts:  a  consider- 
able enlargement,  the  brain,  is  lodged  in  the  cranial  cavity 
of  the  skull,  and  a  long  spinal  cord  occupies  the  channel 
formed  by  the  annular  vertebrae.  The  branches  it  bears, 
and  by  which  it  maintains  communication  with  peripheral 
parts  of  the  body  are  paired  nerves,   which   it  gives  off 


igo  GENERAL    BIOLOGY 

throughout  its  length.  Those  nerves  issuing  through 
openings  in  the  base  of  the  cranial  cavity  of  the  skull 
are  called  cranial  nerves,  and  those  issuing  from  the  inter- 
spaces between  the  vertebrae  are  called  spinal  nerves. 

The  nervous  apparatus  of  the  body  is  composed  of  nerve 
cells  and  their  processes.  Where  the  bodies  of  the  cells 
predominate,  as  in  the  center  of  the  cord  and  in  the  sur- 
face layer  of  the  fore  part  of  the  brain,  they  give  the  nervous 
tissue  a  pale  grayish  cast;  and  where  the  fibres  predominate, 
the  tissue  appears  white  (the  so-called  "gray  matter"  and 
"white  matter"  of  the  nerve  centers) .  We  have  seen  a  very 
simple  sort  of  differentiation  of  nerve  cells  with  processes 
in  the  hydra  (fig.  loi/).  And  in  the  earthworm  (fig.  109) 
we  have  found  them  very  highly  differentiated.  But  in  the 
vertebrates  the  processes  from  nerve  cells  are  often  very 
much  longer  and  the  interrelations  between  them  often 
much  more  complex.  Each  spinal  nerve  consists  of  a 
bundle  of  these  long  processes  or  fibres,  inclosed  in  a  com- 
mon sheath. 

Spinal  nerves  arise  in  pairs  between  the  vertebrae,  as 
already  noted,  each  by  two  roots  (which  are  also  bundles 
of  fibres),  and  out  upon  the  dorsal  root,  just  before  its 
confluence  with  the  ventral  to  form  the  completed  nerve, 
there  occurs  a  little  isolated  cluster  of  nerve  cells:  that  is, 
a  ganglion.  There  are  other  nerve  cells  in  the  organs 
of  special  sense,  and  at  the  termini  of  sensory  nerves  all 
over  the  surface  of  the  body.  The  apparent  branching 
of  the  nerves  is  due  to  the  division  of  the  bundle  of 
fibres  into  lesser  bundles,  and  finally  into  single  fibres 
that  take  different  courses  to  their  appropriate  endings. 
The  fibres  themselves  are  continuous,  and  extend  from 
cells  in  the  cord  or  in  ganglia,  to  other  ganglia  or  to 
peripheral  parts  of  the  body.  They  are  individual  lines 
of    nervous    communication;     they    separate    as  do    tele- 


ORGANIC  EVOLUTION 


191 


a 


graph    lines    in    passing   outward    from     the    commercial 
centres  to  the  remoter  districts. 

Within  the  coelom  of  vertebrates  there  are  other  ganglia, 
in  part  arranged  in  pairs  segmentally  and  connected  with 
the  ventral  roots  of  the  spinal  nerves,  as  shown  in  figure  117, 
and  in  part  variously   disposed  in  the  walls  of   the  internal 

organs  of  the  coelom,  whose  funct- 
ions they  control  and  coordinate. 
These  are  connected  with  each 
other  by  nerve  fibres.  They  to- 
gether constitute  the  so-called 
sympathetic  system.  The  fun- 
damental nutritive  processes  of 
the  body,  that  are  performed 
involuntarily,  and  that  are  es- 
sential to  keep  life  going,  are 
unconsciously  controlled  through 
the  sympathetic  system.  Prac- 
tically all  the  involuntary  mus- 
cles of  the  body,  those  of  the  skin, 
as  well  as  those  of  the  viscera, 
are  controlled  through  nerve 
fibres  that  take  their  origin  from 
the  cells  of  sympathetic  ganglia. 
There  is  another,  more  direct 
line  of  communication  between 
the  organs  of  the  coelom  and  the 
brain.  One  pair  of  cranial 
nerves  (called  the  vagi;  sing,  vagus)  which  descends 
through  the  neck  into  the  coelom,  sends  branches  also  to 
the  lungs,  the  heart,  the  stomach  and  part  of  the  intestine. 
The  movements  of  the  involuntary  muscles  are  com- 
paratively simple  and  uniform,  but  those  of  the  volun- 
tary muscles  of   the   body  wall   and   limbs   are  infinitely 


Fig.  117.  Diagram  illustrating 
the  relation  of  the  neural  tube 
to  the  ganglia  a,  is  a  cross- 
section  of  the  body  showing 
the  sympathetic  ganglia  in 
the  coelom ;  b,  is  a  cross- 
section  of  the  cord  and  adja- 
cent ganglia ;  showing  roughly 
the  location  of  the  groups  of 
nerve  cells. 


192 


GENERAL   BIOLOGY 


varied  and  complex,  and  are  ever  effected  in  new  combina- 
tions. Hence  there  is  a  correspondingly  large  proportion 
of  the  regulative  cells  of  the  body,  the  nerve  cells,  located 
in  the  neural  tube.  The  most  significant  new  feature  of 
cell  grouping  found  among  vertebrates  is  the  aggregation 
of  nerve  cells  at  the  forward  end  of  the  neural  tube  to 
form  the  brain.  The  cord  widens  on  entering  the  skull 
into    the    medulla.      On   its    dorsal  side    a   thin    roofed 


a 


m 


n 


Fig.  118.  Diagrams  of  the  brain  of  the  salamander,  zo, 
dorsal  view;  x,  ventral  view;  y,  lateral  view  and  z,  dia- 
gram of  the  continuous  internal  cavity  in  dorsal  or 
ventral  .view;  a,  olfactory  lobe;  b,  cerebral  hemi- 
spheres" c,  pineal  body;  d,  thalamencephalon;  e,  optic 
lobes; /,  cerebellum;  g,  medulla,  h,  spinal  cord;  i',  in- 
fundibulum;  /,  hypophysis;  ^.lateral  ventricles;  /,  third 
ventricle;    w,   optic    ventricle?;    n,  fourthrventricle. 

V-shaped  slit,  called  the  fourth  ventricle,  exposes  the  cen= 
tral  cavity  that  extends  in  fact  throughout  its  length. 
A  transverse  ridge  of  nervous  tissue  at  the  front  of  the 
fourth  ventricle  upon  the  dorsal  side  is  the  cerebellum.  A 
pair  of  rounded  swellings  just  in  front  of  the  cerebellum  are 
the  optic  lobes.  The  pair  of  large  oblong  lobes  at  the  front 
are  the  cerebral  hemispheres.  These  and  other  parts  exter- 
nally visible  may  be  located  by  reference  to  figure  118. 
Their  relations  to  each  other  will  be  considered  when  their 
development  is  studied  (p.  198). 


ORGANIC    EVOLUTION 


193 


Development. — The  way  of  access  to  intelligent  compre- 
hension of  the  cellular  structure  of  the  salamander  lies 
through  the  study  of  its  development. 

The  salamander  begins  life  as  a  single  cell,  the  result  of 
fusion  of  egg  and  sperm.  It  is  a  very  large  cell,  because 
distended  with  yolk  and  enveloped  by  a  thick  gelatinous 
envelope;  but  the  protoplasmic  part,  the  living  part  of  it, 
is  very  small.  The  protoplasm  is  not  equally  distributed 
through  the  egg,  but  is  more  abundant  on  the  upper  pig- 
mented side.  Therefore,  the  division  planes  in  cleavage 
start  on  the  upper  side,  and  division  is  somewhat  retarded 
below  by  the  impeding  yolk  mass.  The  cell  divides  into 
two  cells  along  a  meridional  plane  and  the  two  divide  into 
four  by  another  meridional  plane  at  right  angles  to  the 
first;  then  the  four  divide  into  eight  by  a  plane  parallel 
to  the  equator  of  the  sphere,  at  right  angles  to  both  former 
planes,  not  at  the  equator,  but  a  little  nearer  the  darker 
upper  pole,  where  it  divides  the  protoplasm  more  equally. 
Successive  meridional  planes,  and  planes  parallel  to  the 
equator  mark  the  following  divisions  into  i6-cell,  32-cell, 
etc.,  stages  which,  however,  are  not  traceable  farther 
because  of  the  retardation  of  division  on  the  lower  side,  and 
because  of  the  planes  getting  ajog  at  the  joints.  The  result 
is  clearly  a  blastula,  as  before — a  hollow  sphere  of  cells  of 
small  size.  The  slipping  inward  from  the  surface  of  some  of 
its  cells  results  in  its  being  more  than  one  layer  in  thickness 
over  part  of  the  upper  side,  and  the  retardation  of  division 
owing  to  excess  of  yolk  on  the  lower  side  throws  the  segmen- 
tation cavity  above  the  middle  of  the  sphere.  All  these 
facts  are  indicated  in  the  accompanying  figures.  Then 
gastrulation  takes  place  in  a  manner  that  is  yet  more 
aberrant.  An  ingrowth  from  the  outer  wall  gives  rise  to 
endoderm  surrounding  an  arch-enteron  as  before ;  but  the 
ingrowth,  impeded  by  yolk  does  not  result  in  a  widely  open 


# 


194 


GENERAL  BIOLOGY 


blastopore,  but,  instead,  a  narrow  crescentic  slit,  the  edges  of 
the  blastopore  being  pressed  together  as  shown  in  figure  iigi. 
Then  the  edges  of  the  crescent  extend  downward  until  they 
meet  below  a  little  circular  patch  of  protruding  yolk,  the  yolk 
plug.  Except  upon  the  upper  side  where  lies  the  direct 
entrance  to  the  archenteron,  they  cut  but  a  shallow  circular 


,<^^^^ 


m 


n 


Fig.  119.  Early  development  of  salamander  eggs,  a  to  h,  i-.  2-, 
4-,  8-,  t6-,  32-cell  and  later  segmentation  or  cleavage  stages;  ?.  7,  gas- 
trulation  stages;  i,  shows  the  crescentic  blastopore  and  /,  the  fully  formed 
yolk  plug;fe  to  m,  formation  of  the  neural  tube. 

groove  upon  the  surface  of  the  yolk.  If  one  conceive  of  his 
own  head  as  the  sphere  of  the  gastrula  salamander,  his 
closed  mouth  the  blastopore,  and  the  corners  of  his  mouth 
pulled  down  until  they  join  beneath  his  chin,  he  will  get  a 
clear  conception  of  the  relation  of  these  parts.  Figure  121 
shows  in  longitudinal  sections  the  formation  of  the  gastrula, 


ORGANIC   EVOLUTION  195 

and  the  formation  and  subsequent  withdrawal  from  the 
surface  of  the  yolk  plug.  The  segmentation  cavity  is 
reduced  in  size  as  the  endodermal  sac  increases  in  depth. 

Then  the  mesoderm  appears  in  the  space  between  ecto- 
derm and  endoderm  at  the  blastopore  on  the  upper  side,  and 
spreads  outward  and  downward  in  a  thin  sheet  of  tissue,  and 
begins  to  split  to  form  a  coelom.  Up  to  this  point  in 
development  it  will  be  observed  that  nothing  has  appeared 
to  suggest  a  vertebrate  animal.  In  the  one  celled  stage  the 
embryo  is  more  like  a  protozoan  in  structural  type ;  in  the 
blastula  stage  it  has  the  hollow  spherical  form  of  volvox; 
in  the  gastrula  stage  it  is  more  like  hydra  in  plan.  As  soon 
as  it  has  acquired  a  compound  tubular  body  through  the 


Fig.  120.     Sections  of  salamander  eggs  in  a  meridional  plane, 
8-cell,  32-cell  and  later  segmentation  stages, 

development  and  splitting  of  a  mesodermal  layer,  it  is  more 
like  a  worm,  and  not  until  the  appearance  of  a  central 
nervous  axis  upon  the  dorsal  side  is  there  a  single  structure 
present  that  can  be  pointed  out  as  distinctively  characteristic 
of  a  backboned  animal.  Thus  the  series  of  embryonic 
forms  assumed  by  the  salamander  in  its  development  shows 
a  rough  correspondence  to  the  series  of  adult  forms  we  have 
been  studying.  Furthermore,  when  vertebrate  characters 
appear  they  are  very  generalized  indeed,  and  the  parts  in 
formatibn  look  no  more  like  the  adult  salamander  than  like 
other  vertebrate  animals. 

Vertebrate   characters. — Several  distinctively  vertebrate 
characters  appear  now  in  different  parts  of  the  body  almost 


196 


GENERAL   BIOLOGY 


c 

.9 

■♦-» 

iS 

'd   . 

o 

be  ^ 
c  '-' 

•c  o 
d 

OJ    to 


(V)  O 


bo 


<^ 


simultaneously.       The    first  to    appear   externally   is   the 
nervous  axis  upon  the  dorsal  side  and  this  and  the  gill  slits 

and  the  notochord  are  es- 
pecially worthy  of  our  consid- 
eration. 

Beside  the  blastopore  an 
elevation  appears  which  rises 
in  two  parallel  ridges  called 
the  neural  folds.  These  folds 
at  their  outgrowing  ends  are 
confluent  in  a  loop  which 
marks  the  head  end  of  the 
salamander.  These  folds  grow 
rapidly,  and  by  their  increase 
in  length  project  from  the  sur- 
face of  the  egg  at  both  ends, 
spoiling  its  spherical  symme- 
try. The  withdrawal  of  the 
yolk  plug  is  accompanied  by 
the  outpushing  of  the  tail  be- 
yond the  end  of  the  neural 
folds.  The  folds  come  togeth- 
er, as  indicated  in  the  accom- 
panying figures,  the  wider  an- 
terior end  becoming  the  brain, 
the  remainder,  the  spinal  cord. 
This  then  sinks  into  the  in- 
terior as  indicated  in  the 
cross-section  diagrams  of  fig- 
ure 122. 

Meanwhile  the  archenteron  is  elongating  in  a  parallel 
direction,  and  a  fold  from  its  dorsal  wall  is  cutting  off  the 
notochord — the  most  ancient  supporting  structure  of  verte- 
brates— a  larval  organ  in  most  of  them  at  the  present  day. 


c  .. 

O  1-1 

l-i   c4 

<u     . 

c  .- 

a  m 

BO) 

o> 

to  ^ 
C  (1) 
O   O 

•^  o 

u 

03 


I— I 


ORGANIC    EVOLUTION 


197 


The  archenteron  is  converted  into  an  alimentary  canal  by  a 

process  somewhat  differing  from  that 
followed  in  the  worm ;  it  is  destined 
to  occupy  a  reversed  position;     tha 

nV\\  blastopore  becomes  the  anus,  and  the 
H I  I  mouth  is  formed  at  the  opposite 
Hi  I  end  by  an  ingrowth  from  the  ecto- 
derm that  meets  the  front  end  of  the 
archenteron  and  fuses  and  then  opens 
a  passage  through.  The  anterior 
end  of  the  archenteron  becomes  dor- 
sally  flattened  and  laterally  ex- 
panded into  a  pharynx,  from  whose 
walls  sacculations  of  endoderm  grow 
outw^ard  to  meet  the  ectoderm,  and 
then  cleave  apart  on  vertical  lines, 
opening  gill  clefts  on  the  side  of  the 
neck.  The  pillars  of  tissue  left 
standing  between  these  clefts  become 
the  gill  arches.  By  these  simple 
processes,  are  laid  down  the  main 
lines  of  vertebrate  structure. 

Endodermal  differentiation. — The 
embryonic  endoderm  becomes 
epithelium,  as  before,  and  is  the  lining 
layer  of  the  alimentary  canal  and  of  its  appendages.  It  is 
for  the  most  part  a  single  layer  of  cells  not  remarkably  modi- 
fied in  form,  differing  in  length  according  to  the  extent  of 
their  compression.  In  the  pharynx  they  are  short-cylindric 
and  ciliated  on  their  free  ends  (figure  134).  In  the  intestine 
they  are  much  more  compressed  and  slender,  and  certain  of 
their  number  are  differentiated  as  goblet-shaped  mucus- 
secreting  cells.  In  the  stomach  where  the  wall  is  made  up 
of .  multitudinous    pit-like   depressions   called    the    gastric 


Fig.  122.  Diagram  of  the 
formation  of  neuron,  no- 
tocord  and  coelom.  The 
ectoderm  is  white,  the 
endoderm  is  soUd  iDlack 
and  the  mesoderm  is 
crosslined;  c  c,  notocord; 
c  n,  pronephric  duct. 


m 


198 


GENERAL   BIOLOGY 


glands,  they  are  differentiated  into  bulky  cells  that  secrete 
the  digestive  fluids  at  the  bottom,  mucus-secreting  cells 
along  the  sides  of  the  pits  and  of  protective  cells  about  the 
mouths  of  the  pits  where  they  come  in  contact  with  the 
food.  In  the  lung,  where  the  extension  of  the  walls  is  very 
great,  the  cells  are  spread  out  flat  and  very  thin  to  cover 
them.  This  thinness  favors  the  diffusion  of  gases  between 
the  blood  and  the  air,  and  is  characteristic  of  respiratory 
epithelium. 

The  liver  arises  very 
early  (fig.  123)  as  a  wide 
sacculation  of  the  archen- 
teron  near  its  anterior  end 
on  the  ventral  side.  This 
outgrowth      becomes 


re- 
peatedly branched,  and 
the  resulting  glandular 
blind  tubules  become  con- 
voluted, the  basal  connec- 

FiG.  123.      Diagram    of    a  longitudinal  sec-   4-;^,^,    rp>mainc    ac    a     clA-nrlAr 
tion   of  a  young  embryo,   n,  neural  tube;   ^^^'^    rcmamb    db    d    bienuer 

^,  enteron,  the  black  spur  from  the  upper    ---riTTn  a  refiner     fn'hp'      fViA     "hilA 
side  represents  the  free  part  of  the  noto-    COnnCCimg     XUDC,    XnC      DUe 

cord.     The  ventral  outgrowth  from  the    ^..pf    o-nrl  tViP  Hiatal  nnrtinn 
front  end  will  form  the  liver.  QUCt,  aUQ  XnC  QlSXai  porxion, 

acquiring  through  meso- 
dermal additions  a  system  of  blood  vessels,  becomes  differ- 
entiated into  the  lobes  of  the  liver.  A  dilatation  on  the  bile 
duct  becomes  the  gall  cyst  (fig.  114).  The  pancreas  arises 
later  but  by  a  simpler  and  somewhat  parallel  development 
arrives  at  its  adult  estate,  when  it  consists  of  a  mass  of 
glandular-walled  communicating  tubes,  which  secrete  the 
most  important  single  digestive  fluid  of  the  body.  The  uri- 
nary bladder  arises  as  a  similar  but  simpler  sacculation  at 
the  posterior  end. 

Development  of  the  neural  tube. — We  have  already  seen 
that  the  central  nervous  axis  develops  into  a  tube  by  the 


ORGANIC  EVOLUTION 


199 


FiG.  124.  A  young  salamander  larva,  show- 
ing gill  slits  (5).  b.  blastopore;  /,  2,  j,  fore-, 
mid-  and  hind-brain,  respectively. 


closure  together  of  two  folds  about  a  neural  groove,  and  that 
the  tube  thus  formed  then  sinks  into  the  body  wall.     The 

diagrams  of  figure  122 
show  how  it  is  over- 
grown, first  by  the 
ectoderm  and  later  by 
mesoderm,  and  re- 
moved from  the  surface. 
The  original  neural 
groove  thus  closed  be- 
comes the  central  canal 
of  the  spinal  cord.  It  is 
lined  with  a  little  bit  of  the  epidermal  layer  of  the  ectoderm, 
carried  in  from  the  surface.  A  small  ridge  of  nerve  cells 
that  arises  each  side  of  the  tube  dorsally  (fig.  122c) 
becomes  divided  with  growth  into  pieces  corresponding  in 
pairs  to  the  body  segments;  and  when  later,  nerves  grow 
out  as  processes  from  the  cells,  these  pieces  become  located 
upon  the  dorsal  roots  of  the  spinal  nerves  and  become  the 
ganglia  (fig.  117)  hitherto  noticed. 

Quite  early  in .  its  development  the  axis  becomes  feebly 
marked  off  into  three  successive  tracts,  which  correspond  to 
the  fore  brain,  mid  brain  and  hind  brain  of  the  adult  sala- 
mander (figs.  124  and  125).  The  fore  brain  becomes  bilobed 
by  a  dilatation  on  either  side  of  the  median  plane,  and  by 


,s-^' 


:*w 


'3. 


^^ 


Fig.  125.     Older  salamander  larva,  showing  gills,  /.  2.  j,  fore-,  mid-  and  hind- 
brain. 


^ 


200 


GENERAL  BIOLOGY 


Fig.  126.     Older  salamander  larva,    showing  further  development  of  the  gills. 
a,  anus;  b,  gills;  c,  opercular  fold;  d,  nostril;  e,  mouth;  /. /,  caudal  fin; 

growth  of  the  two  lobes  forward  and  extension  of  the  ex- 
panded canal  into  them,  the  hollow  cerebral  hemispheres  are 
formed;  the  small  olfactory  lobes  grow  forward  from 
beneath  their  anterior  ends.  At  the  rear  of  the  hemispheres 
on  the  middorsal  line  a  small  process  grows  upward  to 
become  the  pineal  body — a  vestigial  structure,  correspond- 
ing to  the  nervous  apparatus  of  a  median  eye,  that  is 
functional  in  some  lizards.  A  hollow  downgrowth  on  the 
midventral  line  develops  the  infundibulum.  This  connects 
with  the  pituitary  body,  developed  in  the  roof  of  the  mouth. 
Paired  upgrowths  from  the  lateral  wall  of  the  midbrain 
become  the  optic  lobes  of  the  brain.  The  central  cavity 
extends  into  each  of  these,  the  expansions  of  it  within  the 
optic  lobes  being  known  as  optic  ventricles.     An  axial  dila- 


FiG.  127.     Older  larva  of  the  spotted  salamander,  with  legs  developed. 

tation  of  the  central  canal  (fig.  1 18  2;)  is  known  as  the  third 
ventricle.  From  the  front  end  of  the  third  of  the  primary 
brain  divisions  the  cerebellum  arises  as  a  transverse  solid 
upgrowing  ridge  of  tissue  upon  the  dorsal  side.  Just 
behind  this  lies  the  fourth  ventricle,  as  already  noted  (fig. 
iiSw).     It  appears  from  above  as  a  triangular  dilatation 


ORGANIC     EVOLUTION 


20I 


of  the  central  cavity  of  the  medulla ,  but  thinly  covered 
upon  the  dorsal  side. 

The  elongate  brain  of  the  sala- 
mander, with  its  parts  outspread 
almost  like  a  diagram,  is  very 
simple  in  comparison  with  that  of 
the  higher  vertebrates  (fig.  128). 
In  birds  the  cerebellum  and  the  optic 
lobes  are  relatively  larger  and  in 
mammals,  and  especially  in  man, 
the  cerebral  hemispheres  attain  their 
maximum  development. 

Thus  a  simple  tube  of  undifferen- 
tiated nerve  cells  becomes    moulded 
Fig.  i?8.    Brains  a.  of  pigeon  i^to    a    brain.     By    localized    out- 
r'^pL^IrbSdy'^T^'S:  growths  of  its  walls  all  the  principal 
^!^J'o,''^il^''\o^  external  features    of    its    form    are 
p,  optic  lobe.  wrought  out.     The    subsequent  de- 

velopment of  fibres  from  all  these  masses  of  cells  is  a 
matter  far  too  intricate  for  us  to  attempt  to  follow  here. 
A  few  of  the  more  salient  features  of  the  ultimate  distribu- 
tion of  these  fibres  will  be  considered  in   chapter  VII. 

The    development    of    the    primary  circulation. — In    the 

midst  of  the  mesoderm,  tube-like  clefts  appear,  which, 
extending  and  becoming  confluent,  develop  into  the  blood 
vessels.  The  most  important  of  these  appears  as  a  cleft 
of  sigmoid  curvature  in  the  region  of  the  throat,  and  by 
the  processes  diagrammatically  represented  in  figure  129, 
it  becomes  enlarged,  strongly  flexed,  and  divided  into  com- 
partments, it  develops  muscular  walls,  and  becomes  the 
heart.  It  becomes  two  chambered  by  the  difterentiation 
of  an  auricle  and  a  ventricle,  the  former  being  carried  to 
the  front   of  the   latter   by  the  flexion  undergone   during 


10^ 


GENERAL  BIOLOGY 


development.  The  passage  leading  forward  from  the  ven- 
tricle, destined  to  become  the  arterial  trunk,  becomes  con- 
joined with  other  paired  passages  in  the  mesoderm  of  the 

throat  leading  to  the  gills,  which  be- 
come the  branchial  arches.  Corre- 
sponding vessels  develop  upon  the 
dorsal  side  and  become  conjoined 
with  the  great  dorsal  aorta,  leading 
rearward  (see  figures  130A;,  and  131). 
About  the  time  these  vessels  are 
first  marked  out,  gills  develop  upon 
the  gill  arches  externally  (fig.  126) 
and  become  traversed  by  a  system  of 
capillary  vessels,  which  are  at  this 
stage  the  connecting  link  between  the 
dorsal  and  ventral  vessels  just  men- 
tioned. The  circulation  of  the  blood 
through  these  transparent  external  gills 
is  easily  observed  with  the  microscope,  and  it  is  a  beautiful 
sight. 

This  simple  type  of  circulation  is  essentially  fish-like  (fig. 
130;^;).  There  are  no  lungs  as  yet,  and  hence  there  is  no 
pulmonary  circulation.  The  heart  is  but  two  chambered. 
All  the  blood  passes  forward  from  the  ventricle  through  the 
gills,  to  be  returned  rearward  through  the  dorsal  aorta. 
The  aortic  arches  are  four,  and  at  first  essentially  alike. 

Development  of  pulmonary  circulation. — Lungs  develop 
as  already  noted  by  outgrowth  from  the  ventral  pharyngeal 
wall,  and  blood  vessels  to  supply  them  arise  from  the  fourth 
branchial  arch  and  extend  rearward  to  penetrate  their  walls. 
Return  channels  are  developed,  joining  the  lungs  directly 
with  the  heart.  When  these  vessels  become  functional,  a 
considerable  part  of  the  blood  is  diverted  from  the  gills  to 
the  lungs.     This,  however,  is  of  late  occurrence,  being  an 


Fig.  129.  Diagram  of  de- 
velopment of  the  larval 
two  chambered  heart. 
X,  the  primitive  cleft  of 
the  mesoderm;  y,  the 
differentiation  of  cham- 
bers and  valves;  z,  the 
completion  of  the  sig- 
moid flexure;  5,  venus 
sinus ;  a,  auricle ;  v,  ven- 
tricle. 


ORGANIC   EVOLUTION 


203 


accompaniment  of  the  shift  from  aquatic  to  terrestrial  life. 
Before  it  happens  the  gills  begin  to  atrophy  and  new  chan- 
nels begin  to  be  developed.  A  carotid  artery  springs  from 
the  anterior  side  of  the  foremost  branchial  vessel  on  each 
side,  to  carry  blood  from  the  heart  into  the  head.  A  short 
cut  is  developed  between  the  dorsal  and  ventral  portions  of 
the  branchial  vessels  of  the  second  pair,  and  these  become 
the  aortic  arches  of  the  adult  salamander,  forming  a  con- 


FiG.  130.  Diagram  of  types  of  circulatory  apparatus  in  vertebrates  x,  a 
lung  fish  (Ceratodus) ;  y,  a  frog  and  s,  a  mammal.  (For  the  sake  of  clear- 
ness the  auricle  is  turned  backward,  straightening  out  the  sigmoid  flexure.) 
7,  2,  J,  4,  the  four  branchial  arches,  becoming,  in  y  and  s;  i,  the  carotid.  2, 
the  aortic,  and  4,  the  pulmonary  arches;  a,  auricle;  v,  ventricle:  /,  lung;  c, 
cava;  r,  the  single  root  of  the  dorsal  aorta  in  mammals. 

tinuous  uninterrupted  channel  from  the  heart  to  the  dorsal 
aorta,  which  ultimately  becomes  the  main  channel  of  the 
circulation.  Thus  we  see  that  in  metamorphosis  the  fourth 
arch  that  springs  from  the  arterial  trunk  becomes  the  pulmo- 
cutaneous  artery;  the  first  arch  becomes  the  carotid,  the 
second  becomes  the  aortic,  the  third  atrophies,  or  becomes 
variously  connected  with  adjacent  arches,  and  the  bran- 
chial circulation  first  laid  down  becomes  so  altered  as  to  be 
recognizable  only  by  most  careful  comparison. 


204  GENERAL  BIOLOGY 

The  fate  of  the  gill  clefts  and  skeletal  arches  is  no  less 
interesting.  The  foremost  cleft  narrows  to  a  tubular  pas- 
sage way,  in  connection  with  the  outer  end  of  which  the  ear 
is  developed,  and  the  cleft  in  part  persists  as  the  eustachian 
tube  leading  from  the  pharynx  to  the  middle  ear;  this  is  its 
fate  in  most  higher  vertebrates,  and  in  ourselves.  The 
other  clefts  close  after  the  atrophy  of  the  gills.  The  skeletal 
arches  that  surround  the  neck,  standing  between  the  clefts 
have  various  fates.  The  mandibular  arch  that  stands  in  the 
wall  before  the  first  cleft  in  the  salamander,  becomes  the 
mandible,  or  lower  jaw  of  the  adult  salamander  (note  that 
the  tadpole  has  no  mandible,  and  the  form  of  its  mouth  is 
entirely  changed  in  metamorphosis).  The  succeeding 
skeletal  arches  of  the  larval  salamander  persist  in  part  as  the 
paired  members  of  the  hyoid  skeleton  shown  in  figure  112; 
the  foremost  of  these  persists  as  the  single  hyoid  bone  in 
most  of  the  higher  vertebrates  and  in  ourselves. 

The  kidney. — The  development  of  the  kidney  is  no  less 
remarkable.  In  that  part  of  the  cleft  mesoderm,  which 
enters  into  the  composition  of  the  body  wall  (the  somatic 
layer)  a  cleft  appears  which  develops  into  a  long  tube  or 
duct,  (fig.  122  c,  n)  that  extends  from  a  point  on  the  ven- 
tral wall  of  the  archenteron,  where  the  urinary  bladder  will 
later  develop,  forward  along  the  wall  of  the  coelom.  At  its 
anterior  end  several  short  convolute  tubes  develop,  with 
their  open  ends  abutting  against  a  dilatation  of  the  dorsal 
aorta  in  the  coelom  (fig.  131a).  Thus,  they  are  probably 
able  from  the  beginning,  by  reason  of  this  connection,  to 
remove  nitrogen  waste  from  the  blood.  These  tubules  in- 
crease in  number,  length  and  complexity  of  arrangement 
and  form  the  pronephros,  or  "head  kidney." 

The  true  kidney  develops  later,  and  much  farther  back  in 
the  coelom.  It  begins  as  separate  and  isolated  tubules 
developing  against  the  dorsal  wall  along  side  the  pronephric 


ORGANIC  EVOLUTION 


205 


duct,  into  which  they  later  find  admittance.      The  tubules 
(fig.  131c)  increase  in  number  and  differentiate    internally. 


Fig.  131.  Diagram  of  the  development  of  amphibian  gill  slits 
gill  arches,  pronephros  and  kidney,  a,  is  a  horizontal(frontal) 
section  of  the  body  of  a  young  larva,  showing  the  relations 
of  the  newly  formed  pronephros  to  the  dorsal  aorta  in  front 
and  to  the  cloaca  behind;  h,  is  the  hyo-mandibular  gill  cleft. 
/,  2,3,  4,  the  succeeding  four  branchial  clefts;  b,  is  a  dissec- 
tion of  an  older  larva,  showing  the  branchial  blood  vessels, 
and  the  true  kidneys  attaching  to  the  pronephric  duct;  c,  is  a 
diagram  of  a  single  nephridial  tubule  from  the  kidney.  The 
arrows  at  the  left  indicate  the  course  of  the  capillary  blood 
circulation  through  the  glomerulus;  ihe  arrow  at  the  right 
indicates  the  path  of  excreta  to  the  ureter. 

Each  acquires  connection  with  one  of  the  capillaries  joining 
the  renal  arter  y  with  the  post  cava.  All  of  one  side  become 
combined     together  in  a   single   organ,   the   kidney.     The 


206 


GENERAL  BIOLOGY 


rear  end  of  the  pronephric  duct  becomes  the  ureter;     the 
anterior  end,  and  with  it  the  pronephros,  atrophies.     These 


Fig.  132.  The  lancelet  (Amphioxus,  or  Branchiostoma)  after  Gegenbaur. 
a,  mouth;  b,  gill  chamber;  c,  sac  of  enteron  corresponding  to  the  liver  d 
stomach;  e,  intestine'  /,  anus;  g,  aortic  arch;  h,  portal  vein;  i,  notocord, 
with  dorsal  aorta  extended  beneath  it;  ;',  post  eava  (all  the  main  blood 
vessels  have  contractile  walls) ;  k,  coelom. 

changes  are  diagrammatically  indicated  in  figure  131. 

The  skeleton. — In  some  very  primitive  alHes  of  the  true 
vertebrates  (as  for  example,  the  lancelet,  fig.  132),  the 
notocord  persists  through  life  as  the  chief  supporting  struc- 
ture of  the  body ,  but  in  the  salamander  as  in  vertebrates  gen- 
erally, it  is  early  replaced  by  a  cartilaginous  skeleton. 
Its  cells  become  vacuolated,  and  are  finally  resorbed 
and  entirely  disappear.  The  beginnings  of  the  develop- 
ment of    the     cartilaginous  cranium  about   the   front  end 

of  it  are  shown  for  the  sal- 
amander in  gure  133.  Car- 
tilage constitutes  the  whole 
skeleton  of  many  of  the  lower 
fishes,  but  in  the  higher  verte- 
brates it  is  more  or  less  re- 
placed by  bone. 

Study  26.      The  internal  organs 

of  an   amphibian   {frog  or 

salamaiider .) 

Fig.     133.     Front    end  of  notocord 

'^^^'SiV^.^^.^i'^  Materials    needed:       Living 

Sngs'of'carTiia"g1nous ?ranS-.     spccimcns  to  be  examined  as  to 
q.  orbit  of  eye;  r,  notocord.  extcmal    fcaturcs,  appearance 


ORGANIC    EVOLUTION  207 

and  actions.  Freshly  anesthetized  specimens  for  gross 
dissection. 

Study  the  internal  organs  in  the  order  outlined  in  the 
preceding  pages;  (if  fuller  outlines  are  desired,  they  may  be 
found  in  laboratory  manuals  of  vertebrate  zoology  or  of 
general  zoology,  nearly  all  of  which  deal  mainly  with  com- 
parative anatomy) .  Trace  the  alimentary  canal  and  note 
its  differentiation  into  parts.  Identify  its  appendages 
and  find  their  channels  of  communication  with  the  enteron. 

Inflate  the  lungs  and  note  the  relation  between  air 
tubes,  air  cells  and  blood  vessels.  Identify  the  cham- 
bers of  the  heart  and  trace  the  main  channels  of  circu- 
lation. Trace  the  ureter  from  the  kidneys  to  the  mouth  of 
the  urinary  bladder.  Compare  spermaries  and  ovaries  in 
male  and  female  specimens  and  trace  the  ducts  for  the  exit 
of  the  sex  cells. 

Find  the  paired  spinal  nerves  issuing  from  the  spinal 
column  and  lying  against  the  roof  of  the  body  wall,  and  find 
the  paired  sympathetic  ganglia  in  the  coelom  attached  by 
commissures,  one  pair  to  the  roots  of  each  pair  of  spinal 
nerves;  look  also  for  nerves  extending  from  these  ganglia 
to  other  sympathetic  ganglia  in  the  walls  of  stomach,  heart 
or  lurfgs. 

The  record  of  this  study  may  consist  in  drawings  and 
diagrams  of  the  form  and  relations  of  the  principal  organs 
studied. 

Study  2J.  The  structures  of  the  body  wall  of  an  amphibian. 
Materials  needed:  The  specimens  from  the  preceding 
study,  if  preserved  in  two  per  cent,  formalin  after  the 
removal  of  the  internal  organs.  Wash  free  from  the  formalin 
in  running  water  before  using.  Also  skeletons  disarticu- 
lated, and  a  few  mounted  ones  for  comparison.  Also,  some 
forms  with  cartilaginous  crania,  such  as  sharks,  or  large  bull 
frog  tadpoles  for  the  easy  examination  of  the  brain. 


2o8  GENERAL  BIOLOGY  . 

Compare  the  bones  with  the  diagram  of  the  vertebrate 
skeleton  as  shown  on  page  oo  and  then  make  a  diagram  of 
the  skeleton  of  this  amphibian.  The  skeleton  of  fore  and 
hind  feet  will  be  easily  observed  if  the  skin  be  stripped  off, 
the  outside  muscles  cut  off,  and  the  undisturbed  skeletal 
parts  then  cleared  in  dilute  glycerine.  The  relations  of 
bone,  muscles,  nerves  and  skin  will  also  be  seen  in  the  mak- 
ing of  the  preparations. 

To  the  examination  of  the  main  external  features  of  the 
brain  should  be  devoted  the  major  part  of  the  time  alloted 
to  this  study.  In  a  shark  or  a  large  tadpole  the  roof  and 
the  coverings  of  the  brain  are  readily  cut  away,  and  the 
parts  shown  in  figure  1 1 8  will  be  easily  made  out. 

The  record  of  this  study  may  consist  of  diagrams  of 
skeleton  and  brain. 

Study  28.     The  cellular  structure  of  an  amphibian. 

Materials  needed:  A  living  or  freshly  anesthetized  male 
specimen ;  slide  mounts  of  prepared  fragments  of  the  ovary 
showing  eggs  and  egg  follicles;  sections  of  the  stomach 
wall,  the  intestine,  the  lung,  the  skin,  the  kidney,  the  spinal 
cord,  etc. 

The  careful  study  of  sections  is  time  consuming,  especially 
for  a  beginner,  and  little  of  it  can  be  done  in  a  single  period. 
To  expedite  their  examination,  a  number  of  them  may  be 
shown  as  microscopic  projections.  The  student  should  at 
least  examine  and  draw  a  few  living  cells  from  the  fresh 
specimen,  such  as  red  and  white  corpuscles  from  the  blood, 
living  sperm  cells,  ciliated  epithelium  scraped  from  the 
roof  of  the  mouth,  etc.  In  the  sections  from  the  enteron 
and  its  appendages,  the  types  of  epithelium  shown  in  figure 
134  should  be  identified,  and  the  subjacent  muscle  layers,  the 
interpenetrating  blood  vessels  and  the  covering  peritoneal 
layer  of  endothelium  should  be  seen.     In  the  skin  section 


ORGANIC  EVOLUTION 


209 


the  thick  fibrous  dermis  should  be  seen  overlaid  by  the  epi- 
dermis of  several  cell  layers,  and  invaded  by  the  large 
mucus  glands  that  depend  from  and  open  through  the  epi- 
dermis. The  parts  of  kidney  and  spinal  cord  may  perhaps 
be  identified  by  comparison  with  figures  13  k;  and  1176,  re- 
spectively. 


Fig.  134.  Diagrams  of  types  of  epithelium,  a,  ciliated  epithelium  of  the 
pharynx;  b,  isolated  cells  of  the  same;  c,  a  gastric  gland  from  the  stomach 
wall;  m,  its  mouth;  n,  the  contact  layer  at  the  surface;  o,  the  middle  layer 
o^  mucus -secreting  cells;  p,  the  gland  cells  of  the  deepest  part  (pepsinogen 
secreting);  d,  a  single  villus  from  the  wall  of  the  intestine;  q.  goblet  cells 
(mucus-secreting) ;  r,  a  group  of  replacement  cells  (center  of  cell  increase)  ; 
e,  a  single  goblet  cell;  /,  a  bit  of  the  wall  of  the  lung  showing  the  thin 
respiratory  epithelium  (stippled) ;  5,  s,  capillaries  containing  blood 
corpuscles. 

The  record  of  this  study  may  consist  in  a  few  drawings  and 
a  larger  number  of  diagrams  of  the  things  studied. 

Study  2g,     The  early  development  of  an  amphibian. 

Materials  needed:  Egg  masses  of  various  stages  of 
development,  preserved  in  two  per  cent,  formalin;  wash 
out  formalin  before  using. 


2IO  GENERAL    BIOLOGY 

Study  and  diagram  segmentation  and  gastrulation  stages 
and  the  main  features  of  formation  and  closure  of  the  neural 
groove  and  the  development  of  gill  slits  and  gills  as  seen  in 
external  views  of  the  specimens.  The  labor  of  drawing  will 
be  lightened  if  uniform  circles  be  drawn  mechanically  for 
the  earlier  stages,  and  cut  out  forms  be  used  for  outlines 
of  the  later  ones;  or,  if  printed  or  otherwise  duplicated 
outline  figures  be  furnished.  This  may  be  supplemented 
by  microscopic  projection  of  egg  sections. 

The  record  of  the  study  will  consist  in  the  series  of  dia- 
grams made. 

The  salamander,  a  typical  vertebrate. — Because  of  its 
primitive  structure,  the  salamander  serves  well  for  intro- 
duction to  the  study  of  the  vertebrates.  The  parts  we 
have  found  in  it  we  would  find  in  all  the  others,  only  modi- 
fied in  form.  As  it  develops,  so  do  the  others,  in  the  main; 
in  all,  the  principal  organs  are  laid  down  in  like  manner 
and  have  like  relations  to  the  germ  layers,  and  to  each 
other.  Neural  tube,  notocord  and  gill  arches  are  formed 
in  all.  A  two  chambered  heart  and  a  fish-like  cir- 
culation develop  first,  and  a  pronephros,  before  the  true 
kidney;  but  some  develop  much  farther  than  the  sala- 
mander, and  along  very  peculiar  lines.  The  salamander 
ends  its  improvement  of  circulatory  apparatus  with  two 
aortic  arches  doing  precisely  the  same  work;  but  in  the 
higher  groups  of  vertebrates,  birds  and  mammals,  we 
find  one  of  these  arches  has  been  done  away  with  and  the 
other  one  does  the  work  alone;  the  right  one  has  been 
retained  in  birds,  the  left  one  in  mammals  (fig.  1302), 
A  further  improvement  in  birds  and  mammals  is  found 
in  the  four  chambered  heart,  which  with  better  de- 
veloped lungs  makes  possible  a  complete  double  circu- 
lation of  the  blood   (fig.  135),  all  the  blood  passing  through 


ORGANIC    EVOLUTION 


211 


the  lungs  on  each  circuit  of  the  body.  All  the  blood  thus 
gathers  oxygen  on  each  round.  Hence,  these  are  the 
warm  blooded  animals:  these  alone  are  capable  of  sus- 
tained activities  in  cold  climates. 

The  purpose  of  circulatory  apparatus 
is  to  get  the  food  to  the  points  where  it 
is  needed  for  use,  and  to  get  the  waste 
to  points  whence  it  can  be  removed 
from  the  body.  When  the  animal  body 
is  small  and  no  part  of  it  is  far  remov- 
ed from  food  supply,  there  is  little 
need  of  circulatory  apparatus.  The 
amoeba  may  feed  at  any  point  of  its 
body.  In  the  hydra,  the  food  cavity, 
extending  to  the  tips  of  the  hollow  ten- 
tacles and  out  into  the  buds,  is  not  far 
removed  from  any  cell.  Even  in  so 
large  an  animal  as  a  flat  worm  the 
food  cavity  may,  by  means  of  exten- 
sive ramifications,  reach  nearly  every 
part.  But  in  all  the  higher  terrestrial 
forms  of  animals,  the  part  of  the  body 
wherein  food  elaboration  occurs  is  small,  and  the  greater 
part  of  the  body  is  remote  from  food  supply,  and  circula- 
tion of  the  food  is  therefore  necessary.  Likewise,  the 
more  the  nephridia  become  localized  in  the  body,  the  more 
necessary  becomes  circulatory  apparatus,  with  aefinite 
blood  channels  leading  to  them  from  every  part  of  the  body. 
But  there  is  circulation  before  there  are  blood  vessels. 
We  have  seen  it  in  Paramoecium;  many  of  the  lower 
multicellular  animals  also  lack  blood  vessels.  There  are 
body  fluids  occupying  the  interstices  between  the  cell  layers 
and  bathing  all  the  tissues  internally.  These  are  the  media 
through  which  the  internal  exchange  of  food  and  waste 


Fig.  135.  Diagram  of 
double  circulation 
(from  Verworn). 


212 


GEx\ERAL  BIOLOGY 


materials  is  effected.     These  supply  the  aquatic  environ- 
ment that  is  necessary  for    the  maintenance  of   cell   life: 

for  cell  life,  in  the  beginning  aqua- 
tic, is  in  an  important  sense  aqua- 
tic still,  even  in  terrestrial  organ- 
isms. Living  protoplasm  is  a  semi- 
fluid substance,  and  metabolism 
is  compatible  only  with  a  liquid 
state. 

The  fluids  of  the  body  are  moved 
about,  (that  is,  circulated)  in  part 
by  the  movements  of  the  tissues 
which  they  bathe,  and  in  the  higher 
organisms  appear  special  organs  of 
propulsion.  Blood  vessels  at  first 
appear  as  short  open  contractile 
tubes,  that  communicate  freely  with 
the  coelom,  and  that  merely  serve  to 
keep  the  blood  irregularly  moving. 
When,  as  in  the  higher  vertebrates 
they  have  become  completely  closed 
channels,  capable  of  retaining  the 
differentiated  red  corpuscles  and 
carrying  them  about  the  body  in 
continuous  procession,  they  are 
still  supplemented  by  that  inter- 
cellular circulation  that  is  due  to  the 
contraction  of  the  muscles  and 
movements  of  the  organs.  The 
need  of  this  propulsion  of  body  fluids 
by  body  movements  is  convincingly 
evidenced  in  ourselves  by  the  benefit  of  physical  exercise 
(even  though  performed  by  proxy,  as  in  massage),  and 
conversely,  by  the  stagnation  induced  by  too  exclusively 
sedentary  habits. 


Fig.  136.  Diagram  of  the 
two  main  channels  by 
which  food  enters  the 
ge  neral  circulation  in 
mammals.  e,  intestine 
with  villi,  V,  V,  in  its  walls 
r  a,  right  auricle  of  the 
heart,  m,  post  cava;  n, 
precava;  o,  thoracic 
lymph  duct;  ^.pancreas; 
q,  pancreatic  duct;  r, 
hepatic  vein;  5,  portal 
vein;  t,  bile  duct  from  /, 
liver:  arrows  indicate  the 
course  of  secretions  en- 
tering the  intestine,  and 
of  the  absorbed  food  de- 
parting therefrom. 


ORGANIC    EVOLUTION  213 

There  are  more  or  less  definite  channels  {lymph  vessels) 
developed  in  all  the  higher  vertebrates,  for  the  circulation 
of  the  body  fluids  aside  from  the  blood  vessels.  These,  in 
our  foregoing  hasty  survey,  we  have  left  out  of  account. 
But  there  is  one  such  vessel  {the  thoracic  duct)  of  very  great 
importance  in  mammals;  for  by  it  the  greater  part  of  the 
food  enters  the  general  circulation,  in  the  manner  diagram- 
matically  indicated  in  figure  136. 

Aquatic  and  aerial  respiration. — In  water,  the  supply  of 
free  oxygen  is  that  contained  in  the  air  which  the  water  has 
absorbed.  The  simpler  organisms,  being  small,  readily 
obtain  a  supply  by  direct  absorption  through  the  surface  of 
the  body.  Increase  of  size,  however,  disturbs  the  ratio 
between  volume  and  surface  in  the  body.  As  compensation 
for  the  excessive  increase  of  volume,  absorbing  surfaces  are 
increased  by  the  outgro\\i:h  of  gills :  and  then  mechanical 
arrangemxcnts  for  bringing  more  water  into  contact  with  the 
gills  follow.  The  gills  are  lodged  in  respiratory  chambers 
through  which  a  constant  stream  of  fresh  water  is  main- 
tained, but  still  the  amount  of  oxygen  available  is  much 
more  limited  than  in  free  air.  There  are  no  warm  blooded 
animals  except  air  breathers. 

In  the  open  air,  the  oxygen  supply  is  inexhaustible :  but 
air  absorbing  surfaces,  such  as  are  adequate  for  aquatic 
respiration,  cannot  endure  exposure  to  dry  air.  Some  land 
animals  like  the  earthworm,  living  in  moist  places,  are  able 
to  breathe  through  the  skin,  by  keeping  it  moistened  with 
mucus  secretion;  but  if  a  worm  be  exposed  to  a  dry 
atmosphere  it  quickly  dies  of  evaporation. 

The  respiratory  process,  being  essentially  aquatic,  requires 
moist  thin-skinned  surfaces  for  the  intake  of  oxygen,  and 
in  organisms  that  live  in  dry  atmosphere  these  can  only  be 
maintained  inside  the  body;  hence,  the  lungs,  reached  by 
long    tortuous    mucus-moistened    passageways  and  main^ 


214  GENERAL  BIOLOGY 

taining  deep  cavities  next  the  respiratory  epithelium,  where 
a  zone  of  moisture -laden  residual  air  serves  as  a  medium  of 
exchange  and  as  a  buffer  to  the  air  waves  from  the  outside. 

The  amphibians  make  it  easy  to  understand  the  transition 
from  aquatic  to  terrestrial  life  in  vertebrates.  It  would 
have  been  hard  to  imagine  all  the  changes  necessary  for 
fitting  a  fish-like  aquatic  vertebrate  for  life  on  land,  but  in 
a  salamander  these  changes,  some  of  which  would  certainly 
surpass  imagining,  are  all  wrought  out  in  a  little  while 
before  our  eyes;  they  go  forward  without  a  hitch,  and 
most  significant  of  all,  they  go  forward  in  similar  manner, 
in  all  the  higher  terrestrial  A^ertebrates,  whether  they  are  to 
live  any  part  of  their  lives  in  the  water  or  not. 

As  in  the  salamander,  so  in  vertebrates  generally,  the  sexes 
are  separate  and  true  sexual  reproduction  is  universal. 
But  there  is  very  great  diversity  among  them  as  to  mode 
of  nurture  of  young,  and  some  of  the  differences  are  of 
profound  significance.  The  lancelet  (fig.  132)  lays  minute 
eggs  containing  very  little  yolk;  these  segment  and  gas- 
trulate  typically,  and  the  embryos  hatch  when  they  reach 
the  gastrula  stage,  and  thereafter  shift  for  themselves, 
receiving  no  further  parental  nurture.  But  all  the  domi- 
nant groups  of  vertebrates  make  better  provision  for  the 
development  of  their  offspring,  and  do  not  turn  them 
adrift  in  so  immature  and  feeble  and  defenseless  a  con- 
dition. 

Types  of  nurture. — There  are  two  main  types  of  nurture 
for  the  young  of  vertebrates,  i)  The  storing  of  additional 
food  supply  in  the  form  of  yolk  in  the  eggs.  We  have  found 
a  considerable  store  of  yolk  in  the  eggs  of  salamander; 
this  process  reaches  its  maximum  development  in  the 
relatively  huge  eggs  of  birds. 

2)  The  nurture  of  the  young  by  means  of  embryonic 
membranes.     This  reaches  its  maximum  development  in 


ORGANIC  EVOLUTION  215 

mammals,  and  it  has  many  features  of  unique  interest  and 
significance,  but  we  can  here  consider  only  a  few  of  its 
more  general  aspects. 

We  have  already  seen  in  the   salamander  that  a  dilata- 
tion of  the  oviduct  near  its  lower  end  (the  uterus)  serves  for 
the  temporary  storage  of  the    ripe    eggs,    just  before  their 
extrusion.      In  the    higher    mammals    the    two    oviducts 
(called  also    Fallopian    tubes)    become    confluent    at    this 
portion     of     their    length  into  a  single  uterus,    in    which 
the  eggs  on  leaving    the    ovaries    find    lodgment.     Being 
fertilized   internally  they    remain  here,  and  undergo  seg- 
mentation and  other  early  developmental   changes   while 
lying   against   the  uterine  wall.     Almost    as    soon    as   the 
primary  germ  layers   are    established  the  ectoderm    of  the 
ventral  wall  rises  up  about  the  embryo  in  a  circular  fold  all 
about  its     body  and  over  its  back;  the    edges  of  the  fold 
come  together  and  fuse  and  enclose  the  embryo  (or  fatus) 
under  a    double     canopy    of   thin    membrane     called    the 
amnion      (fig.    1376).       Almost    simultaneously    a    food 
absorbing  organ    called    the  allantois  develops  for  at- 
tachment   of   the    embryo  to    the    wall    of    the    uterus. 
This   springs    from  the  endoderm  near   the  posterior    end 
of  the  archenteron.     It  grows  out  as  a  hollow  membranous 
fold  posteriorly  and  then  dorsally  betw^een  the  w4der  folds  of 
the   amnion;     there   is   developed   within   the   allantois   a 
complete  set  of  embryonic  blood  vessels,  the  principal  ones 
being  an  allantoic  artery  that  springs  from  the  great  dorsal 
aorta,  and  an  allantoic  vein  that  returns  the  blood  to  the 
post  cava.     The  allantois  and  the  outer  layer  of  the  amnion 
become  fused  together,  and  attached  to  the  uterine  wall  in  a 
series  of  minute  interlocking  processes    {villi),   the  whole 
complex   attachment   layer  being  known  as  the  placenta. 
The  processes  on  the  wall  of  the  uterus  become  permeated 
by  a  dense  network  of  capillaries  developed  from  the  blood 


2l6 


GENERAL  BIOLOGY 


Fig.  137.  Diagram  of  nurture  of  young  through  embryonic 
membranes,  a,  a  young  embryo  with  embryonic  membranes 
beginning  as  folds  or  outgrowths  of  ectoderm  and  endoderm; 
b,  an  older  embryo  with  the  folds  extending  over  the  back  to 
inclose  the  embryo;  c,  an  older  embryo  with  the  placental 
attachment  to  the  uterine  wall  established ;_  d,  diagram  of  the 
channels  of  food  intake  and  waste  removal  in  the  embryo;  w, 
wall  of  the  uterus;  o,  o,  folds  of  the  ectoderm  which  when 
confluent  form  the  outer  and  inner  amnion;  t,  t,  p  fold  of  the 
endoderm,  outgrowing  to  form  the  allantois;  q,  the  vestigial 
yolk  sac;  r,  the  amniotic  cavi  sac,  in  which  the  embryo  floats; 
s,  gill  slits;  ,  u,  umbilicus;  v,  v,  fore  and  hind  leg  buds;  w, 
the  circulation  through  the  placenta;  m,  indicating  the  course 
of  the  blood  of  the  mother  parallel  to  n,  that  of  the  embryo;  g, 
gill  circulation  of  the  embryo;  h,  heart;  t,  dorsal  aorta,  ;, 
post  cava;  k,  allantoic  artery;  /,  allantoic  vein 


ORGANIC  EVOLUTION  217 

vessels  of  the  mother.  This  becomes  the  source  of  food 
supply  for  the  embryo  during  its  long  prenatal  existence. 
In  the  corresponding  villi  of  the  membranes  of  the  embryo 
copious  capillary  blood  vessels  are  developed  as  a  part  of  the 
e-mbryonic  circulation:  these  are  its  food  taking  organs. 
The  process  of  nutrition  is  one  of  exchange  of  blood  content 
between  mother  and  offspring  by  diffusion  through  the  thin 
walls  of  the  villi.  It  is  quite  comparable  to  the  exchange  of 
gases  which  takes  place  in  the  gills  or  lungs.  Both  food  (in 
solution)  and  oxygen  are  withdrawn  from  the  passing  cur- 
rents of  the  mother's  blood,  and  into  the  same  currents  are 
discharged  the  carbon  dioxide  and  all  other  waste  from  the 
body  of  the  embryo  until  its  birth. 

The  body  of  the  embryo  immersed  within  the  anmniotic 
sac,  closes  to  a  narrow  opening  (the  umbilicus)  on  the  ventral 
side  of  the  abdomen  and  the  closure  elongates  into  a  long 
stalk-like  umbilical  cord  through  whose  vessels  nourishment 
is  drawn  from  the  placenta  until  embryonic  growth  is  ended. 
The  embryo  then  hangs  on  the  cord,  like  a  ripened  fruit  upon 
its  stalk.  At  birth  the  stalk  is  severed,  and  the  feeding 
organs  of  the  embryo,  full  formed  and  functional,  are  called 
into  action. 

Such  are  the  means  by  which  the  maximum  of  provision 
for  development  of  young  is  attained  in  mammals,  and  to 
these  there  is  added  the  development  of  milk  from  the 
mammary  glands  as  a  further  food  supply  for  infancy. 
What  a  vast  difference  exists  in  bodily  equipment  between 
a  new  born  mammal  and  the  microscopic  gastrula  of  a 
lancelet ! 

The  life  process  in  the  salamander  and  in  other  verte- 
brates, is  not  very  different  from  that  in  the  worm.  Indeed, 
it  is  much  the  same  in  its  essentials  in  all  animals,  the  differ- 
ences occurring  in  the  ways  and  means  whereby  these 
are    accomplished.     The    essential    processes   are    compre- 


2l8 


GENERAL  BIOLOGY 


bended  in  the   word    metabolism,  and  their  relation  to  the 
accessory  phenomena  are   indicated  in  the  following  table: 


METABOLISM 


Food  intake 
Digestion 
Circulation 
of  food  from  the 

alimentary  canal 
of    oxygen  from 
the  lungs 

Assimilation  {Ana- 
holism) 

Dissimilation 
{Kataholism) 

Circulation 

of  CO,  and    H^O 

to  the  lungs 
of    H,0    and    N 
waste  to  kidneys 
Discharge  of  waste 


Accessory  processes, 
mechanical  and 
chemical 


The    essential    pro- 
cesses : 

the  work  of  every 
cell 


Accessory  processes, 
mechanical     and 
chemical 


Common  features  of  organization  in  plants   and  animals: 

1.  Protoplasm  is  the  "physical  basis  of  life."  and  in 
nearly  all  organisms  it  is  definitely  organized  into  cells. 

2.  Cells,  therefore,  are  the  units  of  organic  structure, 

3.  The  method  of  increase  is  by  cell  division. 

4.  Every  organism  begins  life  as  a  single  cell. 

5.  Aggregates  of  cells  may  form  individuals  of  a  higher 
order,  with  the  various  parts  of  the  cell  complex  fitted  toge- 
ther in  a  state  of  mutual  dependence. 

6.  Two  processes  are  therefore  involved  in  the  making 
of  such  organisms:   i)  cell  division  and  2)  cell  differentiation. 


ORGANIC  EVOLUTION  219 

7.  The  fitting  of  a  part  of  the  cells  to  perform  special 
functions  follows  the  universal  law  of  specialization,  that 
special  fitness  for  one  thing  involves  limitations  in  respect 
to  other  things. 

8.  The  primary  differentiation  in  all  the  higher  organ- 
isms is  that  into  germ  plasm  and  body  plasm,  the  former 
appearing  in  cells  of  two  complemental  sorts,  eggs  and 
sperms. 

9.  Increase  in  size  of  the  cell  complex  necessitates  sup- 
porting structures  and  circulatory  apparatus,  but  these 
parts  in  the  different  plant  and  animal  groups  are  exceed- 
ingly different  in  structure. 

10.  Exposure  to  the  air  in  terrestrial  organisms  necessi- 
tates the  removal  of  the  organs  for  intake  of  oxygen  from 
the  surface  of  the  body  and  the  development  of  epidermal 
layers  to  withstand  evaporation. 

Besides  these  matters  of  general  organization,  there  are 
many  other  things  pertaining  to  the  functions  of  organ- 
isms, to  the  phenomena  of  growth  and  metabolism,  to  the 
finer  structures  of  protoplasm  and  to  the  behavior  of  its 
parts  in  reproduction,  that  are  common  to  plants  and 
animals.  A  few  of  the  better  known  (cytological)  phenom- 
ena of  the  behavior  of  nuclear  parts  in  reproduction,  will 
be  briefly  noticed  in  the  next  chapter. 

The  simpler  organisms  best  illustrate  the  common  feat- 
ures of  plant  and  animal  organization.  The  forms  we  have 
been  considering  in  Chapter  III  illustrate  rather  a  few  of 
the  main  lines  of  divergence :  but  beneath  their  diversity 
lie  the  common  features  just  stated.  All  living  things  are 
composed  of  one  kind  of  substance,  that  is  organized  into 
equivalent  structural  units,  that  increases  by  one  method 
of  growth,  and  that  reproduces  successive  ganerations  from 
a  common  starting  point. 


220 


GENERAL  BIOLOGY 


The  principal  groups  of  organisms. — In  the  foregoing 
studies  we  have  had  before  us  representatives  of  a  few  of  the 
larger  groups  of  plants  and  animals.     We  have  not  time  to 


LINNAEUS 

(1707-1778) 

A  great  piotleersystematist;  founder  of  the  binomial  system 
of  nomenclature;  author  of  Systema  Naturae   etc. 


develop  a  system  of  classification,  or  even  to  enumerate  all 
the  groups,  but  a  tabular  statement  of  a  few  of  the  larger 
and  more  important  groups  is  given  on  the  following 
page: 


ORGANIC  EVOLUTION  221 

Plants 

I.  Thallophytes,   algae  and  fungi. 
II.  Bryophytes,  liverworts  and  mosses 

1.  Hepaticae,  liverworts 

2.  Musci,  mosses. 

III.  Pteridophytes,    the  ferns  and  their  allies 

1.  Filicinae,  the  true  ferns  and  the  water-ferns 

(Marsilia,  etc). 

2.  Equisetinae,  the  horse-tails 

3.  Lycopodina^,  the  club  mosses,  etc. 

IV.  Spermatophytes,  The  seed  plants 

1.  Gymnospermae,  plants  with  naked  seed ;  conifers 

etc. 

2.  Angiospermae,  plants  with  seeds  developing    in 

closed  vessels 

a)  Monocotyledons 

b)  Dicotyledons. 
Animals 

I.  Protozoa,  one-celled  anim^als. 
II.  Metazoa,  many  celled  animals. 

1.  Porifera,  sponges 

2.  Coelenterata,  polyps,  jelly-fishes,  etc. 

3.  Vermes    (in    broad     sense)   segmented    and 

unsegmented  worms,  rotifers,  bryozoans,  etc. 

4.  Mollusca,  clams,  snails,  squids,  etc. 

5.  Echinodermata,     star-fishes,        sea-urchins, 

holothurians,  etc. 

6.  Arthropoda,  insects,  spiders,  crustaceans,  etc. 

7.  Tunicata ,  tunicates 

8.  Vertebrata,  backboned  animals. 

a)  Pisces,  fishes 

b)  Amphibia ,  frogs ,  salamanders ,  etc. 

c)  Reptilia,  lizards,  snakes, turtles, etc. 

d)  Aves,    birds 

e)  Mammalia,  mammals. 


222  GENERAL  BIOLOGY 

II.       GENERAL    EVOLUTIONARY    PHENOMENA   AS   ILLUSTRATED 
IN      BRIEFER      SERIES     OF     ORGANISMS. 

In  the  foregoing  studies  we  have  given  brief  consideration 
to  a  very  few  plants  and  animals,  selected  to  illustrate  the 
two  main  lines  of  organic  development,  corresponding  to 
the  plant  and  animal  "kingdoms";  but  the  wide  gaps 
between  the  types  studied  haA^e  left  far  too  much  to  be 
bridged  in  imagination.  Hydra  and  earthworm,  or  liver- 
wort and  fern,  stand  so  far  apart  in  point  of  structure  that  it 
is  difficult  to  conceive  of  all  the  forms  intervening.  Let  us 
now  compare  together  some  forms  that  are  more  alike  in 
order  to  see,  if  possible,  the  nature  of  the  relations  organisms 
bear  to  each  other.  In  so  doing  our  attention  will  be  given 
to  typical  organic  phenomena,  rather  than  to  typical  organ- 
isms. These  will  be  grouped  for  convenience  under  three 
heads: 

1.  Divergence  and  convergence  of  development. 

2.  Progressive  and  regressive  development. 

3 .  The  correspondence  between  ontogeny  and  phylogeny. 

I.     Divergence  and   convergence  of  development. 

Whatever  our  views  of  relationship,  the  series  in  which 
we  arrange  organisms  are  based  on  the  likenesses  and  differ- 
ences we  find  to  exist  among  them.  This  is  classification. 
We  associate  organisms  together  under  group  names 
because,  being  so  numerous  and  so  diverse,  it  is  only  thus 
that  our  minds  can  deal  with  them.  Classification  furnishes 
the  handles  by  which  we  move  all  our  intellectual  luggage. 

We  base  our  groupings  on  what  we  know  of  the  organisms. 
Our  system  of  classification  is,  therefore,  liable  to  change 
with  every  advance  of  knowledge.  The  earliest  groupings 
of  animals  were  very  simple  and  obvious;  "creeping 
things,"  "flying  things,"  "fishes  of  the  waters,"  etc.  How 
recently,  indeed,  have  bats  ceased  to  be  grouped  with  the 


ORGANIC  EVOLUTION  223 

birds,  and  whales  with  the  fishes.  That  the  very  many 
different  sorts  of  things  Hving  in  the  water  were  for  a  long 
time  merely  fishes,  is  witnessed  by  the  common  names  they 
still  bear:  shell-fish,  crayfish,  jelly-fish,  cuttle-fish,  etc. 
Such  classification  was  based  on  the  recognition  of  the  most 
superficial  characters  only.  Generally  the  more  funda- 
mental characters  are  the  less  obvious  ones,  and  are  found  in 
internal  organs,  and  in  developmental  phenomena. 

The  earliest  anatomical  classification  of  land  animals, 
based  on  the  number  of  feet — bipeds,  quadrupeds,  hexapods, 
octopods,  decapods,  centipedes  and  millipedes — was 
vastly  improved  when  the  bipeds  and  quadrupeds  and 
fishes  got  together  on  the  basis  of  the  common  possession  of 
a  spinal  column  as  the  group  Vertebrata,  and  all  the  others 
were  dissociated  therefrom  as  Invertebrata.  But  the 
development  of  embryological  knowledge  in  a  later  period 
showed  that  there  are  characters  more  fundamental  than 
the  vertebrae ;  that  certain  of  the  invertebrates  possess  in 
common  with  all  the  vertebrates,  pharyngeal  gill  clefts  and  a 
notocord;  hence  Cordata  replaces  Vertebrata  as  the 
more  comprehensive  group  name. 

Homologies  and  analogies. — Our  judgment  of  the  like- 
nesses between  organisms,  or  between  the  parts  of  a  single 
organism,  is  based  on  that  essential  identity  of  parts  that  we 
call  homology*.  Two  organs  are  homologous  when  com- 
posed of  like  parts  in  similar  relations,  each  to  each.  Thus, 
the  hand  of  a  man  ffig.  261)  and  the  fore  foot  of  a  sala- 
mander (fig.  262)  are  homologous,  since  they  are  com- 
posed of  the   same    parts    put  together  in  essentially  the 


*A  few  exceptional  organisms,  like  certain  bacteria,  are  so  simple 
in  structure  that  differences  in  their  bodily  organization  are  hardly 
discoverable:  and  their  recognition  depends  m  part  at  least  on 
their  manner  of  growth  in  cuUure  media,  and  in  the  nature  of  the 
by-products  of  their  activity. 


224 


GENERAL  BIOLOGY 


same  way.  On  the  other  hand,  when  the  likeness  is  super- 
ficial only,  and  not  fundamental;  when  it  is  likeness  in 
function  or  in  superficial  appearance,  it  is  called  analogy. 
Thus  the  wing  of  a  bird  and  the  wing  of  a  butterfly  are 


LOUIS   AGASSIZ 

(1807-1873) 

A  great  teacher  of  zoology,  who  did  much  to  promote  the 

development  of  science  in  North  America.. 

analogous  organs,  for  though  agreeing  in  form  and  function 
they  are  totally  different  in  structure,  and  have  no  com- 
ponent parts  that  we  can  recognize  as  identical. 

Homology  is  .therefore,  the  ordinary  criterion  by  which  we 
judge  of  the  relationship  of  organisms.     In  the  neck  of 


ORGANIC  EVOLUTION  225 

nearly  all  mammals  there  are  seven  cervical  vetebrae, 
whether  the  neck  be  long  as  a  giraffe's  or  short  as  a  mole's. 
The  foremost  is  the  atlas  vertebra,  and  bears  up  the  skull; 
the  second  is  the  axis  vertebra,  about  which  the  atlas  swmgs; 
the  other  five,  although  less  differentiated,  are  equally- 
constant  in  position  and  relations,  and  we  can  not  doubt  but 
that  these  seven  are  i-dentical.  The  fore  limbs  of  vertebrates 
are  sufficiently  unlike  in  superficial  appearance;  we  know 
them  as  legs  in  most  quadrupeds,  as  flippers  in  seals,  as 
wings  in  birds  and  bats,  and  as  arms  in  ourselves;  but 
when  we  examine  their  structure  we  find  they  are  built  on  a 
common  plan  (fig.  iii),  and  therefore,  hom.ologous.  The 
recognition  of  homologies  often  calls  for  the  utmost  care  in 
comparison  of  organs  and  for  discriminating  judgment  of  a 
high  order.  It  was  a  dictum  of  the  elder  Agassiz  that  the 
education  of  a  naturalist  consists  in  learning  how  to  compare. 

There  is  beside  this  correspondence  of  parts  between 
different  organisms,  a  similar  correspondence  betw-een  parts 
that  are  serially  repeated  in  a  single  organism.  This  is 
called  serial  homology.  It  is  well  represented  in  the  repeti- 
tion of  parts,  segment  by  segment  in  the  earthworm. 

The  student  in  this  course  has  already  had  in  Chapter  I,  a 
little  practice  in  identifying  homologous  parts;  first,  in 
flowers  (pistils,  stamens,  corolla,  etc.),  and  later  in  the  parts 
of  the  body  of  insects.  A  special  study  of  this  matter  is 
given  here  with  material  more  available  for  critical  examina- 
tion. 

The  veins  in  the  wings  of  insects. 

The  veins  that  constitute  the  supporting  frame  work  of 
an  insect  wing  may  bear  the  following  names  and  designa- 
tions: 

Costa  (O      Subcosta  (5c)      Radius         {R) 
Media  (M)    Cubitus    {Cu)     Anal  veins  (.4) 


226 


GENERAL  BIOLOGY 


The  order  in  which  they  are  named  is  that  of  their  arrange- 
ment from  front  to  rear.  Branches  of  veins  are  conveniently 
designated  by  numerals  added  in  like  order  to  the  abbrevia- 
tion for  the  vein  (as  Sc^  and  Sc^  for  the  two  branches  of  the 
subcostal  vein).  But  there  is  one  large  branch  so  distinc- 
tively formed  that  it  has  received  a  special  name,  the  radial 
sector  {Rs) .  All  these  veins  and  their  usual  mode  of  branch- 
ing are  shown  in  solid  lines  in  the  accompanying  diagram  of 
a  typical  wing.  In  dotted  lines  are  shown  the  cross  veins  of 
most  frequent  occurrence.  Tw^o  of  these  toward  the  base 
of  the  wing  the  humeral  cross  vein  (h)  and  the  arculus  (ar) 
have  received  special  names;     the    others  are  named   in 


Sc^ Sr, 


^*^  T~  i't,     Cu 


M 


Fig.  138.     Diagram  of  the  venation  of  an  insect  wing. 

accordance  with  the  positions  they  occupy  in  relation  to 
the  veins.  The  radial  cross  vein  (r)  and  the  median  {m) 
occupy  the  principal  forks  of  the  radial  and  median  veins 
respectively,  and  radio-median  (j-nt)  and  medio-cubital 
(m-cu)  connect  the  veins  whose  names  they  bear. 

These,  then,  are  the  materials  with  which  Ave  have  to 
deal  in  the  following  exercise.  While  they  appear  simple 
and  distinct  enough  in  the  diagram,  a  glance  at  the  three 
series  of  wing  figures  shows  that  it  is  not  at  once  easy  to 
be  certain  as  to  their  identity.     For; 


ORGANIC  EVOLUTION 


227 


First,  nature  has  not  made  the  cross  veins  visibly  to 
differ  from  the  bases  of  branches,  and  the  angulated  and 
transverse  base  of  a  branch  may  look  like  a  cross  vein.  It 
will  help  in  settling  their  identity  to  note  carefully  the  type 


8 


10 


II 


Fig.  139.     The  venation  of  the  wings  of  a  series  of  craneflies.     /,  Limnophila; 
2,  Cylindrotomi;  ^,  Liogma;  4,  Anisomera;  j,  Cienophora;     6,  Dolichopeza; 
7,  Acyphona;(S,  Ula;  9,  Mongoma;  /o,  Oropeza;  //,  Erioptera. 

of  branching  of  the  veins.  The  radial  sector  springs  from 
the  posterior  side  of  the  radial  stem,  and  is  typically  twice 
forked,  as  is  also  the  median  vein,  while  the  subcostal  and 
cubital  veins  are  but  once'forked. 


228 


GENERAL  BIOLOGY 


Second,  there  are  fewer  veins  in  most  of  the  wings  figured 
than  in  the  diagram.  Veins  may  disappear  through  fusion 
of  two  or  more  branches  into  one,  or,  more  rarely,  by  atro- 
phy. Fusions  may  occur  between  branches:  a)  from  the 
tips  approximated  on  the  wing  margin,  proximally  to  the 
forks;  b)  from  the  forks  distally  to  the  wing  margin,  or  c)  by 


Fig.  140.  Venation  of  the  wings  of  various  flies  (order  Diptera).  a,  Rhyphus;  &, 
Conops;  c,  Erax;  d,  Dixa;  e,  Xylophagus ; /,  Thereva;  g,  Eristalis;  /j.  Stratiomyia, 
All  from  Comstock. 


the  elimination  of  a  cross  vein  through  confluence  of  branches 
of  adjacent  veins,  and  subsequent  fusion  distally  to  the  wing 
margin.  Various  stages  of  progress  in  all  the  methods  of 
disappearance  of  branches  will  be  found  in  the  wings  figured 
herewith. 


ORGANIC  EVOLUTION 


229 


Study  JO.     Determination  of  homologies  of  wing   veins   in 
three  series  of  closely  allied  insects. 

Materials  needed:  Enlarged  prints  of  the  wings  figured 
herewith  (or  of  any  other  series,  showing  like  phenomena), 
and  a  single  mounted  wing  of  the  common  cranefly,  Tipula, 
with  which  to  begin. 


8 


10 


II 


Fig.  141.  Venation  of  the  wings  of  a  series  of  Psocids.  /,  Thyrsopsocus;  2, 
Dictyopsocus;  j,  Taeniostigma;  4,  Epipsocus;  j,  Ptilopsocus;  6,  Myopsocus;  7, 
Psocus;<S,  Peripsocus;  g,  Polypsocus;  /o,  Calopsocus;  //,  Ca;cilius. 


230  GENERAL  BIOLOGY 

First,  draw  the  wing  of  Tipula,  carefully,  to  see  the  nature 
of  the  material  under  consideration;  for  the  others,  to 
save  time,  use  the  figures,  which  are  reasonably  accurate. 

Then  begin  with  the  cranefly  wings  series.  Carefully 
label  the  veins  in  each  wing  with  the  proper  abbreviation  at 
base  and  apex;  do  this  lightly  in  pencil,  subject  to 
later  correction.  Mark  fusions  of  branches  with  the  plus 
sign  between  the  numerals  of  the  branches  conjoined. 
Determine  homologies  carefully.  Follow  each  main  vein 
stem  outward  and  see  when  and  how  often  it  forks.  The 
proof  of  correctness  will  consist  in  having  all  parts  of  the 
typical  wing  present  or  accounted  for.  Omit  to  name  a 
vein  or  branch  only  when  it  is  considered  to  have  disappeared 
by  atrophy;  in  this  series  and  the  next  following,  veins  M4 
and  3d  A  may  be  so  treated.  Note  particularly  that  the 
cross  veins  are  all  in  their  proper  places,  or  accounted  for. 
When  correctly  interpreted  the  series  will  be  consistent 
and  harmonious,  and  the  correctness  of  it  will  be  obvious. 

Finish  the  work  by  coloring  the  veins  alternately  in  two 
different  colors,  and  making  the  cross  veins  a  third  color. 

Repeat,  with  the  second  series  of  miscellaneous  fly  wings. 

Repeat  with  the  third  series,  of  psocid  wings,  (fig.  141) 
noting  here  in  the  beginning  that  median  and  cubital  veins 
are  fused  together  in  all  members  of  the  series  from  near  the 
base  outward  well  across  the  wing. 

The  record  of  this  study  will  consist  in  the  one  drawing 
and  in  the  coloring  and  lettering  of  the  veins  on  the  prints, 
and  these  are  to  be  preserved  as  material  to  be  used  in  a 
subsequent  study. 

The  serial  homology  of  the  higher  crustaceans. 

Serial  homology  is  characteristic  of  the  group  of  the  higher 
Crustacea  known  as  the  sub-class  Malacostraca,  and  this 
group  well  illustrates  how  a  single  plan  of  structure  may  run 


ORGANIC  EVOLUTION 


231 


through  a  series  of  forms  of  the  utmost  diversity  in  appear- 
ance, and  how  parts  essentially  alike  may  be  adapted  to  the 
most  diverse  ends. 

The  Malacostracan  body,  be  it  an  amphipod,  an  isopod,  a 
decapod,  or  what  not — is  composed  of  a  series  of  twenty* 
segments,  each  of  which  is  essentially  of  the  skeletal  plan 
shown  in  the  diagram  (fig.  142),  except  that  appendages  of 
the  foremost  segment  are  typically  unbranched  and  the 
hindmost  segment  (the  telson)  is  rudimentary  and  bears 
no  appendages  at  all.     Some  of  these  segments  may  become 

fused  together  and  consolidated  on 
the  dorsal  side,  only  the  appendages 
and  ventral  margins  remaining  free. 
This  may  occur  at  either  end  of  the 
body,  but  it  occurs  constantly  in 
the  five  front  segments,  these  by 
fusion  forming  the  head.  The  ap- 
pendages of  these  five  segments 
always  consist  of  two  pairs  of 
antennae  at  the  front,  one  pair  of 
mandibles  beside  the  mouth,  and 
two  pairs  of  maxillae  following  the  mandibles.  These  parts 
and  their  functions  will  readily  be  understood  because  of 
their  likeness  to  the  parts  bearing  the  same  names  in  the 
insects  already  studied.  Immediately  following  the  maxillae 
are  one  or  more  pairs  of  maxillipeds,  likewise  directed  for- 
ward beneath  the  mouth  to  assist  in  the  manipulation  of 
the  food.  Then  follow  legs  and  swimmerets  in  more  or  less 
variety,  the  terminal  joints  of  some  of  the  legs  being  modi- 
fied in  many  cases  into  highly  specialized  grasping  organs 
called     chelipeds,   and    the   swimmerets  being    frequently 


Fig.  142.  Diagram  of  a  cross 
section  of  the  skeleton  of 
a  typical  body-segment  of 
a  malacostracan,  with  its 
appendages;  b,  basipo- 
dite;  e  x,  exopodite;  en, 
endopodite. 


*This  is  not  counting  a  vestigial  segment  in  the  head  region, 
that  is  discoverable  only  during  embryonic  life,  and  with  which 
we  have  here  no  concern. 


232 


GENERAL  BIOLOGY 


modified  to  sen^e  reproductive  or  respiratory  functions. 
The  eight  segments  following  the  head  constitute  the  thorax 
and  the  seven  last  segments  (counting  the  rudimentary  20th 
segment) ,  the  abdomen. 

The  typical  crustacean  appendage  consists  of  a  single  solid 
basal  piece  (basipodite)  and  two  jointed  branches  arising 

therefrom,  one  on 
the  outer  side  {exo- 
podite)  and  one  on 
the  inner  {endopo- 
dite) .  This  typical 
structure  is  best 
shown  by  the  swim- 
merets  of  the  abdo- 
men. Crustaceans 
being  primitively 
f  r  e  e-swimmin  g 
aqua+'O  animals,  it 
is  their  swimming 
appendages  that 
are  least  altered  by 
adaptation.  The 
'  egs  are  the  stoutest 
of  the  appendages, 
and  these  offer  but 
one  branch  arising 
from  the  basal 
piece,  and  that 
composed  of  a  re- 
duced number  of 
highly  differentia- 
ted segments.  A  comparison  of  a  leg  with  the  last  maxilli- 
pede  in  the  crawfish  will  show  which  appendage  has  been 
lost  and  which  preserved  and  specialized.     The  best  clues 


Fig    143.     A  common  crawfish.     (Cambarus). 


ORGANIC    EVOLUTION 


233 


to  interpretation  of  homologies  in  any  appendage  are  likely 

to  be  found  in  other  adjacent 
appendages,  which ,  because  of  prox- 
imity, have  been  subject  to  some- 
what similar  influences. 


Study    ji.     Observations    on   plas- 
ticity of  form  and  persistence 
of  type  in  Malacostraca. 

Materials  needed:  Specimens 
preserved  in  formalin  of  represen- 
tative of  at  least  three  orders  of 
Malacostraca,  Cambarus  (fig.  143), 
Asellus  (fig.  144),  and  Gammarus 
(fig.  145):  if  such  marine  forms 
as  Mysis  (fig.  158a)  and  Squilla 
and  any  of  the  crabs  are  available, 
all  the  better.  Also,  a  few  females 
of  each  type,  bearing  eggs,  and 
a  few  live  specimens  for  use  in  de- 
termining the  functions  of  the 
appendages.  Also,  slide  mounts 
of  such  appendages  as  are  too 
small  to  be  readily  examined  in 
place,  or  easily  removed. 

Observe  the  living  specimens, 
noting  especially  the  different  uses 
to  which  the  appendages  are  put  in 
locomotion. 

Demonstrate  the  very  special 
water-propelling  function  of  the 
"gill  scoop"  that  is  appended  to  the 
outside  of  the  second  maxilla  in  the 
crawfish,  by  holding  the  point  of  a 
copying  pencil  in  the  water  beside 


Fig.  144.  Asellus  aquaticus 
(after  Bars),  a,  dorsal  view; 
o,  ventral  view  of  abdomen 
of  female;  x,  last  segment 
of  thorax  ;:V,  appendage  of 
abbreviated  first  abdomi- 
nal segment  (the  second 
segment  is  without  appen- 
dages in  the  female) ;  2,  gill 
cover  (operculum). 


234 


GENERAL  BIOLOGY 

Table  of  Malacostracan  Appendages 


KINDS  OF  APPENDAGES 

On   Segments 

In   DECAPOD 

In   AMPHIPOD 

In  ISOPOD 

Etc. 

I 

ex:  Antennae 

2 

<  < 

• 

3 

Mandibles, 

4 

etc. 

5 

6 

7 
8 

• 

9 

lO 

1 1 

12 

13 

14 

^5 

i6 

17 

i8 

19 

20 

Bracket  together  the  segments  that  are  consolidated  upon  the  dorsal  side. 
When  different  in  the  two  sexes  divide  the  space  with  a  diagonal  line  and  write 
characters  of  male  and  female  in  separately. 

the  base  of  a  hind  leg  of  a  living  specimen  until  it  dis- 
solves a  little,  and  watching  for  the  colored  water  to  appear 
at  the  front  of  the  animal  when  expelled  from  the  gill  cham- 
ber. The  passageway  through  the  gill  chamber  from  the 
rear  and  outward  at  the  front  may  be  looked  up  later  in  a 
dead  specimen. 

Examine  gill-covers  and  gills  of  Asellus  in  action  by 
turning  a  living  specimen  over  on  its  back  and  watching 
them  under   a  lens.      Note   their  texture   and   form,   and 


ORGANIC  EVOLUTION 


235 


their  typically  paired  arrangement.  The  gills  of  Gammar- 
us  are  appended  to  the  bases  of  the  thoracic  legs  on  the 
inner  side. 

Study  the  segmentation  of  the  body  and  examine   the 

appendages  in  series,  carefully,  in  the  several  types,  with 
the  aid  of  the  mounted  slides  where  necessary,  and  fill 
out  a  table  of  homologies  prepared  as  indicated  on  the 
preceding  page. 

Then  make  out  a  table  of  functions  for  the  appendages  of 
the  several  types,  as  indicated  below,  basing  it  first  of  all 
on  what  you  have  observed  of  the  uses  of  the  several  organs 
while  studying  the  living  specimens.  Legitimate  inferences 
as  to  functions,  may  be  drawn  from  the  form  and  location 
of  appendages. 

Table   of  functions   of  malacostracan   appendages. 


"i 

E 

■r-l 

C/3 

'B. 
>— 1 

C 

m 

l-i 

o 

Chewing    and 
Manipulating  Food 

o 

+-> 
oJ 
u 

a 

For 
:           Orientation 
(tactile) 

Other 
Functions* 

u 

nS 

-4-* 

c 

+-> 
H 

Oh 

Cambarus 

Gammarus 

Asellus 

Etc. 

♦Specify  functions  in  foot  notes. 

Indicate  segments  by  number  only  (i  to  20),  as  in  preceding  table. 

Specify  characters  of  male  and  of  female  separately,  where  they  differ. 


236 


GENERAL  BIOLOGY 


The  record  of  this  study  will  consist  in  the  two  completed 
tables  just  outlined,  together  with  a  few  brief  statements  as 
to  the  relative  uniformity  or  divergence  of  the  appen- 
dages of  particular  segments  or  particular  regions  of  the 
body,  with  possible  reasons  therefor. 

Divergent  development  has  already  been  illustrated  by 
both  the  major  and  the  minor  series  of  forms  that  we  have 

been  consider- 
ing. Indeed,  in 
all  these,  but  es- 
pecially in  the 
two  main  series, 
the  divergence  is 
greater  than  has 
been  specifically 
pointed  out;  for 
the  lower  types 
in  each  series 
represent  in 
themselves  the 
termini  of  their  own  lines  of  development,  and  not  mere 
passing  stages  to  higher  forms.  The  table  of  classification 
on  page  221  is  but  a  statement  of  the  main  lines  of 
divergence. 

Phylogeny. — The  forms  of  a  single  line  of  descent  consti- 
tute a  race,  or  a  phylum.  The  study  of  phyla  is  called  phylo- 
geny. A  common  device  for  expressing  gra  phically  one's  con- 
ception of  phylogeny  is  the  so-called  "genealogic  tree."  The 
generalized  forms  are  placed  near  the  base  of  the  tree,  the 
specialized  forms,  out  at  the  tips  of  the  longest  branches, 
and  the  intermediates  are  arranged,  according  to  one's  con- 
ception of  relationship  ,  somewhere  in  between.  The  student 
who  has  done  the  work  of  the  last  two  practical  studies  will 


Fig.  145.     Gammarus  fasciatus  (after  Paulmier). 


ORGANIC   EVOLUTION 


237 


understand  that  the  tracing  out  of  natural  ph;)  i,  e  /en  with 
abundant  material ,  is  a  matter  of  great  difficulty,  and  that 
when  forms  are  insufficient  and  relationships  not  clear  it 
admits  of  great  diversity  of  opinion,  and  makes  errors  of 
interpretation  easy. 

The  divergence  of  development  stated  in  the  systematic 
table  on  page  221  may  be  more  graphically  presented  to  the 
mind  if  the  groups  contained  therein  be  arranged  in  such  a 
diagram  as  is  shown  in  figure  146.  Such  graphic  represen- 
tations of  the  possible  course  of  evolution  have  been  much 
used  in  the  past,  in  spite  of  their  purely  hypothetical 
character;  and  although  less  comnionly  employed  now, 
still  they  are  an  excellent  aid  to  the  mind  in  grasping  the 
idea  of  genetic  relationships. 


B»^«S     /  KV/V'P<VM\A>« 


Fig.  146.     A  jjenealogic  tree ;     a  graphic  mode  of  illustrating  possible  relation- 
ship between  organisms. 


238  GENERAL  BIOLOGY 

Study  J2.     An  attempt  at  interpreting  a  possible  phytogeny . 

Materials  needed :  The  completed  drawings  from  study 
30,  with  homologies  fully  determined  and  verified. 

Construct  a  genealogic  tree  for  each  of  the  three  series, 
that  shall  show  a  possible  genetic  relationship  (based  only 
upon  the  data  furnished  by  the  venation  of  the  figures). 
Assume  that  the  wing  of  figure  138  is  primitive.  Pick  out 
the  form  most  like  it  to  go  near  the  foot  of  each  tree.  Single 
out  in  each  series  the  different  ways  in  which  the  type  has 
been  modified,  and  make  as  many  principal  branches  as 
there  are  different  kinds  of  divergence.  Pick  out  the  most 
specialized  forms  for  the  tips  of  the  longest  branches. 
Arrange  the  others  in  position  in  accordance  with  their 
degrees  of  divergence,  and  let  the  branching  and  the  length 
of  the  twigs  represent  this.  Derive  no  form  directly  from 
any  other  that  is  in  any  respect  more  generalized.  Compare 
all  wings  in  each  series  together  with  respect  to  each  charac- 
ter, the  divergence  of  the  tips  of  the  subcosta,  the  fusion  of 
the  tips  of  the  first  fork  of  the  media,  etc.  Remember  that 
each  species  is  the  end  of  Its  own  special  line  of  development, 
and  place  each  at  the  end  of  a  twig. 

The  record  of  this  study  will  consist  in  three  genealogic 
trees  (w^hich  may  be  combined  into  one) ,  drawn  without 
any  superfluous  branches  and  with  all  the  forms  figured 
(including  Tipula,  drawn)  located  thereon. 

It  need,  perhaps,  be  stated  concerning  genealogic  trees, 
that  they  generally  err  in  being  more  explicit  than  the 
known  facts  warrant.  The  figure  of  a  tree  does  not  present 
a  good  likeness  of  evolution  as  it  lies  before  us  at  the  present 
time,  because  the  branches  of  the  tree  are  conjoined  in  per- 
fectly definite  relations.  Lines  of  development  are  in  fact 
traceable  backward  only  a  little  way,  and  are  then  lost  in  ob- 
scurity.    The  liverwort  shown  in  figure  147  presents  a  truer 


ORGANIC  EVOLUTION 


239 


picture  of  evolution  as  we  see  it  now.  Some  of  the  main 
branches  are  clearly  conjoined;  others  stand  in  doubtful 
relationships.  The  ultimate  origin  of  all  of  them  is  obscure, 
for  many  of  the  older  parts  have  perished.  There  is  a 
general  divergence  of  the  tips,  but  there  is  also  convergence, 
and  even  crossing.  But  there  are  enough  long  stretches  of 
unbroken  growth  to  leave  no  doubt  as  to  the  general  course 


Fig.    147.     A  leafy  liverwort. 

of  progress,  and  there  is  enough  convergence  of  all  lines 
backward  to  indicate  that  all  the  branches  may  have  sprung 
ultimately  from  a  common  source. 

Group  radiation. — Perhaps  the  most  striking  of  the 
phenomena  of  divergent  development  is  that  which  has  been 
called  adaptive  radiation.  This  name  serves  to  designate 
that  tendency  seen  in  the  members  of  all  the  larger  groups 
of  organisms  to  become  adapted  to  different  natural  func- 


2  40 


GENERAL  BIOLOGY 


tions,  and  to  take  on  structural  peculiarities  suited  thereto. 
The  phylogenetic  lines  radiate  outward,  as  it  were,  from 
common  structural  type,  into  forms  adapted  to  herbiv- 
orous or  car- 
n  i  V  o  r  o  u  s 
aerial  or  aqua- 
tic, or  other 
more  special 
modes  of  hfe. 
Feeding  and 
locomotion 
are  the  two 
general  ani- 
mal functions 
that  require 
the  mo  St 
special  tools 
(fig  148).  The 
accompany  - 
ing  marginal 
figures  will 
serve  to 
bring  to  mind 
how  very  di- 
verse are  two 
such  organs, 
beak  and  feet, 
in  birds.  Any 
dom  in  a  n  t 
major  divi- 
sion of  the 
animal    king- 


PiG.  148.     Beak  and  feet  of  common  birds,  typifying  their  respective  families, 
a,  hawk;  h,  grouse;  c,  catbird;  d,  woodpecker;  e,  sandpiper.  /,  duck 


ORGANIC  EVOLUTION 


241 


Fig 


149.  Hawaiian  birds  of 
the  family  Drepanidas  (after 
Jordan  and  Kellogg).  /, 
Oreomystis;  2,  Pseudones- 
tor;  J,  Heterorhynchus;  4, 
Hemignathus;  J,  Chloridops. 


dom,  even  single  orders  when  of 
dominant  types  (such  as  the  great 
order  Coleoptera  of  insects ,  1 50 ,000 
species) ,  will  furnish  equally 
striking  illustrations.  Indeed  the 
best  examples  of  adaptive  radia- 
tion are  furnished  by  small  groups 
that  are  dominant  within  a  restric- 
ted range.  The  family  Drepanidae 
of  birds  in  the  Hawaiian  islands  is 
such  an  example.  The  singing 
birds  of  these  islands  are  all 
members  of  this  single  family. 
All  are  much  alike  in  internal  struc- 
ture, and  in  all  essential  family 
characters,  but  they  differ  much 
among  themselves  in  form  of  beak 
(fig.  149)  and  in  other  minor 
characters,  as  the  accompanying 
outline  figure  of  a  few  representative 
selected  forms  will  clearly  indicate. 
These  differences  are  correlated  with 
much  greater  differences  in  feed- 
ing habits  than  are  usually  found 
among  the  members  of  a  single 
family.  In  our  own  fauna,  for 
example,  this  order  of  birds 
(Oscines)  is  represented  by  a  num- 
ber of  families:  the  families  of  the 
thrushes,  the  finches,  the  orioles,  the 
warblers,  the  sparrows,  etc.,  in  each 
of  which  there  is  found  one  form  of 
bill,  and  a  general  family  resemb- 
lance. But  the  single  family 
Drepanidae,  in  exclusive  possession 


242 


GENERAL  BIOLOGY 


of  the  Hawaiian  field,  without  competition  except  among 
its  own  members,  appears  to  have  been  developed  along 
many  divergent  lines  in  adaptation  to  all  the  natural  func- 
tions that  are  fulfilled  by  all  the  families  of  the  order 
elsewhere;    and   there     are  stout    seed-cracking   finch-like 


,^t. 


••*►■ 


^..la^iA--.'  . 


..iij........ 


Fig.  150     Swift  and  swallow  (drawn  for  this  book  by  Mr.  L.  A.  Fuertes). 

beaks,  and  slender  leaf-searching  warbler-like  beaks,  and 
many  other  forms  of  beaks  possessed  by  the  different 
members  of  the  one  family.  A  like  diversity  of  group 
development  upon  a  larger  scale  is  found  among  the 
pouched  mammals  (marsupials)  of  Australia,  and  another 
example  among  the  cat  fishes  (Siluroids)  of  South  America. 


ORGANIC  EVOLUTION 


243 


Convergence. — Convergence  of  development  is  less  com- 
mon than  divergence,  probably  because  divergent  lines, 
radiating  outward  from  a  common  starting  point,  are  more 
likely  to  enter  vacant  territory,  and  thus  avoid  the  stress 
of  competition. 

Convergence  is  manifest  in  the  superficial  resemblance 
of  forms  that  are  in  essential  characters  widely  different.  A 
familiar  example  is  furnished  by  the  swift  and  the  swallow 
(fig.  150),  birds  so  similar  in  appearance  and  habit  as  to  be 
readily  confused  by  a  novice;  indeed,  they  were  long 
classified  together  by  ornithologists.  But  they  differ  in 
nearly  every  essential  character,  and  are  members  of  differ- 
ent orders  of  birds.  A  comparison  of  their  feet  will  reveal 
some  of  the  more  obvious  external  differences.  Those  of  the 
swallow  are  of  the  song-bird  type  of  covering;  a  series  of 
overlapping  scales  down  the  front  of  the  "tarsus"  and  a 
single,  sharp-edged  plate  behind.  (Compare  the  tarsus  of  the 
catbird  figure  147c.)  And  the  toes,  counting  from  the  hind 
toe  outward  are  successively  2-,  3-,  4-  and  5-jointed.  The 
tarsus  of  the  swift  is  "rather  skinny  than  scaly,"  and  the 
toes,  taken  in  the  same  order,  are  2-,  3-,  3-  and  3 -jointed. 
Moreover,  the  tail  feathers  of  the  swift  are  spiny  tipped,  as 
in  the  woodpeckers,  with  which  it  has  more  affinity  than 
with  the  song  birds. 

Study  J  J.     A  comparison  of  convergent  species. 

Materials:  It  is  perhaps  inadvisable  to  specify  particular 
illustrative  material  here,  since  any  teacher  may  have  his 
own  "best  illustrations"  of  this  phenomenon,  which  he  will 
regard  as  most  available.  The  following  good  examples, 
will,  however,  be  found  readily  procurable  almost  any^vhere: 
i)  a  bird  and  a  bat,  to  be  compared  for  the  parallel  develop- 
ment of  organs  of  flight.  2)  Two  limpet-shaped  insect  larvae 
common  in  rapid  streams,  the  "water  penny,"  (larva  of  a 


244 


GENERAL    BIOLOGY 


beetle  Psephemts  lecontei)  and  the  larva  of  the  netwinged 
midge  (Blepharocera)  to  be  compared  as  to  form  of  body, 
adapted  to  clinging  to  rocks) :  or,  3)  in  similar  rapid  waters, 
the  immature  stages  of  mayflies  of  the  genus  Heptagenia 


> 


V"-' 


Fir,.  151.      Photoqraoh  of  a  fossil  dragonfly  in  the  Museum  of  Comparative 
Zoology   at  Cambridge,   Mass. 

and  of  stoneflies  of  the  genus  Perla. 

A  special  phenomenon  of  parallelism,  affecting  more 
superficial  characters  will  be  studied  in  chapter  VI  under 
the  name  of  mimicry. 


ORGANIC    EVOLUTION 


245 


The  record. — Enumerate  carefully  the  points  of  similarity 
in  the  two  forms  compared.  Then  make  separate  lists 
of  the  distinctive  group  characters  of  the  two  which  show 
them  to  belong  to  two  different  lines  of  development. 


Fig.  152.  Wings  of  two  living  dragonflies,  for  comparison  with  fig.  151.  The 
upper,  Anotogaster  (family  Aeschnidae) ;  the  lower,  Orthetrum  (family 
Libellulidae). 

2.     Progressive  and  regressive  development. 

As    a    general    phenomenon,    progressive    development 
needs  here  no  further  presentation.     It  has  been  illustrated 


246  GENERAL   BIOLOGY 

by  the  first  section  of  this  chapter,  and  the  figure  on  page  237 
is  a  map  of  evolutionary  progress.  This,  however,  is 
hypothetical.  It  is  a  conception  of  what  may  have  hap- 
pened since  life  appeared  on  the  earth.  How  shall  we  know 
what  actually  has  happened? 

Palaeontology  offers  the  actual  record  of  the  past  history 
of  organisms.  This  record  consists  in  their  fossil  remains, 
buried  and  preserved  in  the  crust  of  the  earth.  It  is  a  very 
fragmentary  and  incomplete  record;  for  only  the  hard 
parts  of  organisms  are  capable  of  preservation  in  the  rocks. 
Therefore,  the  more  soft-bodied  and  primitive  forms  dis- 
appear, and  leave  no  trace.  The  parts  preserved  as  fossils 
are  fragments,  merely,  of  organisms;  shells  of  molluscs; 
teeth  and  bones  and  armor  plates  of  vertebrates;  wings 
and  legs  of  insects,  leaf  and  stem  prints  of  the  larger  plants. 
The  uncovering  of  such  specimens  demands  the  greatest 
care,  and  the  study  of  them  demands  the  greatest  knowl- 
edge of  corresponding  parts  in  living  forms.  Yet,  notwith- 
standing the  necessary  defects  of  the  material,  the  best 
specimens,  and  more  especially,  the  best  series  of  specimens, 
are  of  the  highest  scientific  value.  The  degree  of  perfection 
seen  in  the  preservation  of  structures  even  so  delicate  as  the 
venation  of  an  insect's  wing,  is  truly  remarkable  when  one 
considers  the  long  processes  of  fossilization  through  embed- 
ding in  sedimentary  rocks.  Figure  1 50 ,  for  example,  is  from 
a  photograph  of  a  fossil  dragonfly.  It  is  a  mere  impression 
upon  the  surface  of  a  slab  of  lithographic  stone  from  a 
Bavarian  quarry,  but  how  completely  are  most  details  of 
the  venation  preserved.  Even  a  novice  would  have  no 
difficulty  in  determining  with  which  of  the  two  living  forms 
whose  w4ngs  are  figured  beside  it  (fig.  151)  the  fossil  form  is 
allied. 

Although  palaeontology  has  only  the  hard  parts  to  deal 
with,  every  trace  of  nerve  and  muscle  and  every  other  vital 


ORGANIC  EVOLUTION  247 

part  having  vanished,  yet  the  case  is  not  so  hopeless  as 
might  at  first  appear,  for  the  hard  parts,  although  dead 
parts,  are  the  permanent  defences  and  supports  which  the 
living  substance  has  fashioned,  in  accordance  with  its  needs 
and  hereditary  tendencies.  The  living  substance  in  every 
group  builds  its  hard  parts  on  architectural  lines  of  its  own, 
and  the  parts  of  organisms  are  so  correlated  that  missing 
parts  may  often  be  inferred  from  those  that  are  known. 
The  scattered  bones  of  a  fossil  vertebrate  tend  to  reassemble 
themselves  in  the  mind  of  the  palaeontologist ;  there  is  but 
one  way  in  which  they  will  go  together  consonantly  to  form 
a  possible  organism;  finding  that,  a  picture  of  the  living 
organism  arises  vividly  in  his  mind;  and  if  he  draw  it  on 
paper,  it  is  what  we  call  a  restoration. 

It  would  take  us  too  far  from  the  field  of  our  practical 
studies  of  living  organisms  were  we  to  attempt  to  consider 
even  briefly  the  vast  wealth  of  knowledge  of  extinct  forms 
of  life  that  palaeontology  has  brought  to  light.  For  such 
information  recourse  must  be  had  to  the  text  books,  or  to  the 
chapters  on  palaeontology  in  general  treatises  of  zoology  and 
botany.     We  may  say  of  organisms,  as,  in  another  sense, 

the  poet  Bryant  said  of  men, 

"All  that  tread 
The  globe,  are  but  a  handful  to  the  tribes 
That  slumber  in  its  bosom." 

Hosts  of  forms,  many  of  them  highly  specialized,  and 
some  groups  once  dominant  have  entirely  disappeared  from 
among  the  living,  and  the  aspect  of  existing  groups  has 
vastly  changed  during  the  course  of  their  racial  history. 

The  imperfection  of  the  palaeontological  record  pro- 
ceeds not  so  much  from  its  being  based  on  hard  parts , 
as  from  the  fact  that  the  more  primitive  and  more 
significant  organisms  lack  such  parts,  and  are ,  therefore , 
dropped  from  the  record,  while  the  more  specialized,  although 
having  that  degree  of  hardness  which  renders  them  best 


248 


GENERAL     BIOLOGY 


preserved,  are  the  forms  that  are  least  instructive  as  to 
genetic  relationships.  But,  notwithstanding  these  things, 
the  record  is  clearly  one  of  progress  in  differentiation  of 
parts  and  in  complexity  of  organization.  Seed  plants  and 
back-boned  animals  are  absent  from  the  older  strata  of  the 

earth's  crust. 
The  forms  at 
present  living 
are  most  like 
jr  the  later  fossils, 

and  the  farther 
we  go  back 
among  the  older 
strata,  the  more 
unlike  existing 
forms  do  the 
fossils  become. 
Synthetic  types 
abound:  i.  e., 
forms  combining 
characters  of 
two  groups  that 
are  in  their  liv- 
ing representa- 
tives sharply 
separated.  Such 
a  type  is  the 
famous  Arche- 
opteryx  (fig. 
153)  whose  dis- 
covery brilliant- 
ly fulfilled  Hux- 

FlG.   153.     Archaeopteryx  (after  Zittel).     d,  clavicle;         ^^Y  ^      prediction 
CO,  coracoid;  sc,  scapula;  h,  humerus;  r,  radius;  u,  /'Kacorl      n-n    nr\m 

ulna;  c,  carpus;  /.  //.  Ill, IV.  digits.  J^DdSeu     on  CUm- 


ORGANIC  EVOLUTION 


249 


parative  anatomy)  that  the  groups  of  birds  and  reptiles 
would  be  found  to  be  confluent  in  origin.  Archeopteryx 
is  a  bird  possessed  of  teeth  and  a  long  tail,  and  other 
structural  characters  more  like  to  modern  reptiles  than  to 
modern  birds. 

Among  fossils  there  are  occasionally  found  more  or 
less  continuous  series  of  forms,  successively  more  prim- 
itive in  the  successively  older  geologic  formations.  To 
American  palaeontology  belongs  the  credit  of  discovery  of 


Fig.  154.     Archaeopteryx:  a  restoration  (after  Flower). 


250 


GENERAL   BIOLOGY 


/ 


Fig.  155.  Diagram  illustrating 
the  skeleton  of  the  foreleg  of 
the  modern  horse,  (g)  and  a 
series  of  fossil  forms  (a  to  /)  ap- 
parently illustrating  its  phylo- 
geny;  A, humerus;  r, radius;  ul, 
ulna;  c,  carpus;  ph,  phalanges; 
a,  Orohippus;  b,  Mesohippus; 
C,  Miohippus;  d,  Protohippus; 
e,  Pliohippus;  /,  Equus,  the 
modern    horse. 


one  of  the  most 
famous  of  these, 
illustrating  the 
phylogeny  of  the 
horse.  Possible 
stages  in  the  de- 
velopment of  the 
single  toed  hoof  of  the  horse  as  found  in  fos- 
sils are  represented  in  figure  155.  And  it  may 
confidently  be  believed  that  more  such  series 
would  be  found  were  the  fossils  better 
known.  Palaeontology  is  continually  fill- 
ing the  gaps  between  the  sundered  groups 
of  recent  species. 

The  persistence  of  the  unspecialized. — In 
spite  of  the  abounding  testimony  of  palaeon- 
tology that  throughout  the  history  of  organ- 
isms the  strong  and  the  well-equipped  have 
frequently  dropped  out  of  the  race  for  life, 
and  in  spite  of  the  obvious  structural  advant- 
ages of  the  higher  types  as  we  have  studied 
them  in  the  first  part  of  this  chapter  we  still 
have  amoebas  and  other  very  simple  organ- 
isms flourishing  in  our  midst.  How  have 
they  withstood  the  stress  of  competition 
with  forms  that  appear  to  be  so  much  better 
equipped  ?  Why  have  they  not  all  been  ex- 
terminated? It  may  not  be  possible  to  say 
how  any  particular  organism  has  succeeded, 
but  we  do  well  to  remember,  first,  that  size 
and  specialization  and  organization  have 
their  disadvantages  as  well  as  their  advant- 
ages, and  second,  that  most  specializations 
occur  in  adaptation  to  removal  into  new  fields 


a 


ORGANIC  EVOLUTION  251 

or  into  new  spheres  of  activity.  Great  size  may  entail 
great  peril  in  times  of  scarcity  of  food.  It  takes  much 
food  to  nourish  a  large  organism.  A  dozen  rabbits  may 
fatten  where  one  buffalo  would  starve.  Specialization 
always  means  fitness  for  one  set  of  conditions,  and  is  apt 
to  be  disadvantageous  when  conditions  are  suddenly 
altered.  Complexity  of  organization  is  always  a  peril.  A 
horse  may  fall  and  break  its  neck,  but  hardly  may  a  hydra. 
The  mechanism  with  fewest  parts  and  least  complicated 
adjustments  is  the  one  that  will  best  stand  rough  usage. 

This  persistence  may  be  further  ilkistrated  by  an  analogy. 
Reaping  machines  have  had  an  evolution,  almost  within 
our  own  time.  The  forms  that  have  successively  appeared 
(and  that  have  successively  been  dominant)  are  the  sickle, 
the  scythe,  the  cradle,  the  reaper  and  the  binder,  and  these 
form  a  series,  so  to  speak,  of  increasing  size,  efficiency  and 
complexity  of  structure.  The  advent  of  each  new  form  has 
only  limited  the  field,  has  not  crowded  out,  its  predecessors. 
All  are  in  use  still.  The  larger  machines  are  adapted  only 
to  broad  and  open  fields;  the  cradle  that  once  reaped  the 
fields  is  now  restricted  to  the  stump-patch  or  rocky  hill 
slope;  and  the  sickle  fimds  its  place  in  the  edging  of  the 
shrubbery  or  the  comer  of  the  garden.  All  persist  together, 
and  the  simplest  of  them  is  likely  to  persist  longest. 

In  the  second  place,  these  simple  aquatic  organisms  have 
remained  in  their  primitive  haunts  of  safety,  in  the  ooze  of 
the  bottom,  or  among  sheltering  stems  or  rocks,  where 
more  or  less  out  of  the  way  of  direct  competition  with 
stronger  forms,  and  where  no  sort  of  cataclasm  could  well 
annihilate  their  whole  tribe .  These  circumstances ,  combined 
with  a  good  reproductive  capacity,  make  for  persistence. 

Regressive  development. — This  is  the  phenomenon 
generally  known  as  degeneration.     Retrograde  development 


2  52  GENERAL  BIOLOGY 

in  whole  organisms  has  occurred  most  frequently  as  an 
accompaniment  of  the  parasitic  manner  of  life,  and 
parasites,  therefore,  furnish  its  best  illustrations.  These 
will  be  the  subject  of  a  special  study  in  a  succeeding  chapter; 
but  retrograde  development  in  the  parts  of  organisms  may 
be  noted  here.  An  excellent  example  has  already  been 
before  us  in  the  vestigial  fifth  stamen  of  Chelone  (fig.  23r) : 
and  the  figwort  family  to  which  this  plant  belongs,  would 
furnish  a  series  of  forms  showing  all  grades  of  development 
of  this  stamen  from  normal  functional  development  to  com- 
plete atrophy.  Most  functionless  organs  that  are  found 
larger  and  better  developed  and  functional  elsew^here,  are 
vestigial  structures.  They  are  developmental  heirlooms; 
useless  and  unnecessary,  but  handed  down  by  heredity. 
There  is  no  other  explanation  for  their  existence. 

Often  the  disappearance  of  their  function  has  accompanied 
a  change  of  habit  or  of  habitat  on  the  part  of  their  possessor. 
Thus  the  abundant  stomates  of  the  bladderwort,  useless  and 
imperforate,  although  composed  of  the  two  guard  cells  as  in 
aerial  plants,  have  doubtless  been  carried  over  from  aerial  into 
aquatic  life.  The  bladderwort  (Utricularia)  is  descended 
from  terrestrial  plants,  but  now  lives  wholly  submerged 
beneath  the  surface  of  the  water.  Many  such  shifts  have 
taken  place  in  the  phylogenetic  development  of  the  human 
body.  The  greatest  of  them  must  have  been  from  water  to 
land,  from  horizontal  to  erect  attitude,  and  more  latterly, 
from  savage  to  civilized  conditions  of  living ;  and  the  vestigial 
structures  are  so  numerous  in  man's  body  that  it  has  been 
called  "a  museum  of  antiquities."  The  best  know^n  of 
these  waning  organs  of  vanished  function  are  the  vermi- 
form appendix,  the  muscles  for  wagging  the  ears,  the  "wis- 
dom teeth,"  and  the  hairy  covering  of  the  skin.  Admir- 
able examples  of  such  organs  are  the  rudimentary  lung 
and   pelvic  girdle  of  the  snake. 


ORGANIC  EVOLUTION 


253 


Retrogression  with  change  of  function. — When   a  waning 
organ  loses  its  original  function,  it  may  be  saved  by  being 

put  to  a  new  use.  Thus  certain 
of    the     smallest    innermost 
branches  of    the  our  common 
hawthorns  have  a    brief  exis- 
tence as  leafy  branches  and  be- 
come transformed  into  stout  de- 
|/*^-— ^iiw  j|  '-^g^,,^^M|      fensive  spines  (fig.  156)  which 
r       ■  W^^t^S^Lt^^^Kk      then  serve  the  tree  by  oppos- 
ing the  browsing   of  cattle. 
The  vanishing  fifth  stamen  of 
Chelonehas,  in  the  allied  genus 
Pentstemon,  ceased  to  be  a  poll- 
en bearing  organ,   but  has  be- 
come extraordinarily  developed 
to  aid  in  pollen  distribution  (fig. 
157).     It  is  declined  across  the 
base  of  the  other    stamens, 
elongated  and  protruded  in  such 
position  that  the   entering  bee 
walks  over  its  hairy  tip,  and  in 
so  doing  shakes  the  pollen  from 
the    anthers  of  the  other  sta- 
mens down  upon  its  own  back. 
Specialization    by   reduction. 
— It  is  important  to  note  that 
the  dwindling  and  loss  of  parts 
is   generally   a    gain    to    their 
possessors.     Organs   are  of   no 
moment  except  as  they    serve 

Fig.  156.      Hawthorn  spines    in  the         ,  .  ,^,  , 

making,    a,  compound  spines,     the  organism.      i  he  thrcc  scrics 

formed    from    branches    bearing  r    •  -  i  •  i 

well  developed  leaves;    6,  simple       OI    mSCCtS  WhOSC  WmgS  WChaVC 
spines  formed  from  short  branch-  ,       ^^      ^         ^^  i  i  •1-^ 

es  with  vestigial  leaves.  Studied    all     show     decided 


254 


GENERAL  BIOLOGY 


improvement  in  capacity  for  sustained,   speedy  and  well 

directed  flight,  as 
the  reduction  of  re- 
dundant, and  the 
readjustment  of  the 


remaini  ng 


veins 
proceeds.  It  is  a 
sign  of  a  generalized 


^^'^^::^^.,r,.^sjMM^/Mi^.    condition    when 
^  many    parts    of    an 


organism  are  found 
performing  similar 
functions.  The 

earthworm  is  very 
generalized  in  the  almost  unending  repetition  of  like  parts 
in  successive  segments.   The  malacostracan  Mysis  (fig.  156a) 


Fig.  157.  Beard  tongue  (Pentstemon  pubescens). 
a,  a  flower  viewed  from  the  side;  b,  the  same 
with  the  side  of  the  corolla  cut  a.way,  showing 
the  elongated,  declined  and  hairy  fifth  stamen; 
arrow  indicates  the  path  of  the  entering  bee. 


Fig.  158.      Mysis  stenolepsis  (after  Paulmier). 
b,  A  mud  cra.b.     (Panopsus  depressus). 


ORGANIC  EVOLUTION  255 

is  a  crustacean  similar  to  those  we  had  before  us  in 
study  3 1 ,  but  much  more  generalized  in  the  possession  of  a 
long  series  of  similar  swimming  appendages,  many  of  which 
have,  in  other  malacostracans  been  modified  into  legs, 
nippers,  maxillipedes,  opercula,  stylets,  etc.,  or  altogether 
atrophied  (as  in  the  abdomen  of  the  crab,  fig.  1586),  with 
good  results.  The  horse-development  series  of  figure  155  is 
clearly  a  reduction  series,  and  quite  as  clearly  a  series 
illustrating  the  perfecting  of  the  single  hoof  as  an  organ  for 
rapid  locomotion  on  land. 

J.     The  correspondence  between  ontogeny  mid  phytogeny. 

As  phylogeny  signifies  the  development  of  the  race,  so 
ontogeny  signifies  the  development  of  the  individual.  The 
study  of  ontogeny  is  the  special  province  of  embryology, 
and  investigations  in  this  field  have  brought  to  light,  in 
all  the  great  groups  of  organisms,  abounding  examples 
of  likeness  in  plan  of  structure  of  developmental 
stages  of  higher  forms  to  that  of  adult  organisms 
lower  in  the  same  series.  This  we  have  already 
noted  in  the  salamander.  It  begins  life  as  a  single  cell. 
Its  structure  roughly  corresponds  to  that  of  a  protozoan. 
It  is,  of  course,  as  much  a  salamander  and  as  little  a  proto- 
zoan at  that  stage  as  it  ever  will  be.  But  its  plan  of  bodily 
organization  is  very  like  that  of  a  spherical  single-celled 
protozoan,  and  very  unlike  that  of  an  adult  salamander. 
By  segmentation,  a  blastula  is  formed,  which  is  very  like 
Volvox  in  plan,  since  both  consist  of  a  hollow  sphere  of  cells. 
Then  the  process  of  gastrulation  makes  of  it  a  gastrula, 
which  is  much  like  a  hydra,  in  that  there  are  now  two  layers 
of  cells  surrounding  a  simple  food  sac.  The  correspondence 
between  gastrula  and  hydra,  it  must  be  noted,  extends  only 
to  general  body  plan — not  at  all  to  the  specialized  parts  of 


256  GENERAL   BIOLOGY 

the  mature  hydra;  it  is  rather  to  a  late  embryonic  form  of 
the  hydra,  but  to  one  old  enough  to  show  the  final  plan  of 
hydra  structure  established. 

And  so  the  wonderful  process  goes  forward,  yielding  by 
the  simplest  means  results  that  not  the  boldest  imagination 
could  ever  have  conjectured"^.  Each  new  feature  reveals 
some  characteristics  of  a  higher  type,  and  each  is  soon 
merged  with  others  still  newer.  The  mesoderm  appears, 
and  cleaves  apart  to  form  the  coelom.  Then  neural  tube 
and  notochord,  a  heart  upon  the  ventral  side  and  gill  slits 
appear,  and  it  is  evidently  a  vertebrate.  But  at  first  it 
appears  to  be  a  vertebrate  of  very  primitive  type.  It  has 
gills,  and  a  two  chambered  heart,  and  a  fish-like  circulation. 
Then,  more  slowdy,  as  we  have  already  seen,  these  characters 
are  merged  into  those  we  call  amphibian,  and  finally  it 
appears  in  the  completed  form  of  a  salamander,  consonant 
in  general  with  its  species  and  tribe,  and  in  particular  with 
its  immediate  ancestors,  in  form  and  feature,  in  proclivities 
and  habits,  in  faculties  and  in  action. 

What  a  marvel  of  potentialities  is  the  egg  cell !  What  a 
marvel  of  performance  is  the  simple  cell-mass  we  call  an 
embryo,  that  races  down  the  main  travelled  road  of  its 
phylogenetic  history,  never  going  astray  though  countless 
paths  diverge,  and  only  slackens  its  speed  when  nearing 
its  proper  destination! 


*"Is  it  the  egg  which  the  hen  loves?  .  .  .  How  should  birds 
know  that  their  eggs  contain  their  young?  There  is  nothing,  either 
in  the  aspect  or  in  the  internal  composition  of  the  egg,  which 
could  lead  even  the  most  daring  imagination  to  conjecture  that  it 
was  hereafter  to  turn  out  from  under  its  shell  a  living  perfect  bird. 
The  form  of  the  egg  bears  not  the  rudiments  of  resemblance  to 
that  of  the  bird.  Inspecting  its  contents,  we  find  still  less  reason, 
if  possible,  to  look  for  the  result  that  actually  takes  place.  If  we 
should  go  so  far,  as,  from  the  appearance  of  order  and  distinction 
in  the  disposition  of  the  liquid  substances  which  we  noticed  in  the 
egg,  to  guess  that  it  might  be  designed  for  the  abode  and  nutri- 
ment of  an  animal,  (which  would  be  of  very  bold  hypothesis),  we 
would  expect  a  tadpole  dabbling  in  the  slime,  much  rather  than  a 
dry,  winged,  feathered  creature." — Paley. 


ORGANIC  EVOLUTION  257 

The  development  of  the  salamander  is  but  one  example 
of  that  correspondence  between  embryonic  forms  and 
general  plans  of  adult  structure  that  is  exhibited  in  all  the 
groups.  The  study  of  this  correspondence  by  embryologists 
gave  rise  to  the  "biogenetic  law"  (which  is,  rather,  a  rule 
with  many  exceptions),  that  "Every  animal  in  its  develop- 
ment tends  to  repeat  in  embryonic  stages  the  successive 
types  of  structure  of  animals  lower  in  the  series  to  which  it 
belongs."  But  this  is  only  a  tendency,  due  to  common 
origin,  and  a  common  mode  of  development.  The  corres- 
pondence is  always  remote,  as  we  have  seen;  not  to 
details  of  adult  structure,  but  to  the  simplest  expression  of 
the  structural  type,  and  it  may  be  perverted  by  any  cause, 
internal  or  external,  that  can  modify  developmental  stages 
independently.     It  is  commonly  obscured: 

i)  By  abbreviation  of  the  ontogenetic  record.  Develop- 
mental stages,  normal  to  the  higher  members  of  a  phylum, 
may  be  dropped  out  of  ontogeny.  Thus  the  free-swimming 
nauplius  stage,  common  to  most  of  the  Crustacea,  does  not 
appear  (as  a  free-swimming  stage)  in  the  development  of  the 
crawfish ;  it  is  passed  over  in  the  egg  before  hatching. 

2)  By  the  com.ing  into  predominance  in  growth  of  some 
part  of  late  acquisition  in  phylogenetic  history.  The 
development  of  the  brain  in  the  higher  vertebrates  is  cer- 
tainly of  this  precocious  sort.  The  huge  brain  of  the 
embryo  of  a  bird  or  a  mammal  can  by  no  means  be  regarded 
as  primitive,  although  it  early  develops  to  great  size  in  the 
embryo. 

3)  By  independent  specialization  of  some  of  the  develop- 
mental stages.  This  is  of  the  commonest  occurrence  with 
free  living  larvae,  which  may  be  specialized  in  relative 
independence  of  adults.  The  balancers  of  salamander 
larvae,  present  in  one  species  of  Ambystoma  (A.  punctatum) 
and  absent  in  another  closely  allied  species  {A.  tigrinum) 


258 


GENERAL  BIOLOGY 


are  examples  of  this.  Many  others  will  be  seen  when  a 
variety  of  insect  larvae  illustrating  types  of  metamorphosis 
are  before  us  in  study  41.  The  immature  stages  of  mayflies 
offer  a  superb  example.  The  adults  are  much  alike  in  form 
and  in  habits,  but  adult  life  is  very  brief  and  is  concerned 
only  with  reproduction.  But  the  immature  stages  are 
wonderfully  unlike,  being  fitted  for  life  in  all  sorts  of  waters. 
They  have  specialized  independently. 

The  study  of  embryology  furnished  a  new  criterion  of 
homology.     In  addition  to  correspondence  in  parts  and 


t+3 


**S 


Fig.  159.     Wing  of  the  nymph  of  a  stonefly  (Nemoura)  showing  tracheae,  or 
air  tubes,  of  the   wing,    with   the    veins    developing  about  them   and  be- 
tween them;  note  the  absence  of  tracheae  from  cross  veins,  and  the  lesser       ' 
angulation  of  the  tracheae  than  of  the  veins. 

relations  of  parts  in  adults  fundamental  likeness  has  to  be 
judged  also  by  correspondence  in  development.  This  is 
indeed  the  sort  of  likeness  that  shows  how  deep  seated  is 
the  homology — the  likeness  that  goes  back  to  correspondence 
in  mode  of  origin. 

Embryology  has  also  vastly  extended  the  field  in  which 
homologies  may  be  determined ;  for,  owing  to  the  primitive 
conditions  prevailing  in  the  embryos,  their  parts  may  often 
be  readily  compared  and  seen  to  be  identical,  when  in  adult 
organs  all  likeness  has  disappeared.  That  the  coracoid 
process  of  the  human  scapula  is  in  reality  the  equivalent  of 


ORGANIC  EVOLUTION  259 

the  separate  coracoid  bone  of  the  vertebrate  shoulder  girdle 
is  at  once  evident  when  its  development  is  studied;  for  it 
arises  as  a  separate  bone  and  has  at  first  the  usual  position 
and  relations  of  the  coracoid,  and  later  becomes  anchylosed 
with  the  scapula.  Such  difficulties  as  exist  in  determining 
what  are  the  principal  veins  of  the  wing  of  an  insect,  and 
what  is  the  mode  of  their  branching,  disappear  when  one 
studies  in  the  immature  wing  of  a  primitive  insect,  such  as 
the  stonefiy  shown  in  figure  159,  the  arrangement  of  the 
tracheae,  about  which  subsequently  the  veins  are  formed. 

The  correspondence  between  ontogeny  and  phylogeny 
suggests  an  explanation  of  hosts  of  vestigial  structures 
found  in  embryos.  They  are  inheritances  out  of  the  past. 
Such  are  the  rudimentary  incisor  teeth  of  cattle  w^hich 
though  present  in  the  embryo  never  cut  the  gums,  and  are 
wanting  in  the  adult  animal.  Some  of  them  are  useless  old 
heir-looms,  of  no  practical  consequence;  and  many  of  them 
are  of  no  value  save  as  they  condition  the  development  of 
other  parts.  Such,  also,  are  the  gill-pouches  of  bird  and 
mammal  embryos ;  these  appear ,  only  to  disappear  again 
(save  the  foremost  slit,  in  connection  with  which  the  eusta- 
chian tube  of  the  ear  is  developed),  and  no  gills  are -formed 
in  connection  with  them. 

Ontogeny  often  explains  the  absence  in  the  adult  of 
parts  that  might  be  expected.  Thus,  the  carpus  of  a  bird 
appears  to  be  represented  by  but  two  bones,  if  we  study  only 
the  bones  of  the  adult  bird;  but  in  the  young  bird  an 
additional  row  of  separate  carpal  bones  is  found  (fig.  159) 
in  much  the  same  relations  as  in  other  vertebrates. 

The  tendency  of  the  indiA^idual  in  its  development  to 
repeat  and  reproduce  ancestral  characters  is  but  the  out- 
ward sign  of  that  inward  force  we  designate  as  heredity — 
the  force  which  tends  to  make  like  produce  like.  Perhaps 
it  is  only  a  sort  of  developmental  inertia.     Racial  history 


2  6o 


GENERAL  BIOLOGY 


Fig.  159.     The  wing  bones  of  a  fowl,  a,  adult  grouse ; 
b,  young  dack  (after  Coues). 


flows  on  in  the  old  channels  in  absence  of  obstructions 
sufficient  to  turn  it  aside.  And  the  channels  are  guarded 
from  outside  influences  by  the  protection  that  most  living 
species  give  to  their  young  during  a  portion  of  their  develop- 
ment. We  have 
already  seen  in 
both  plant  and  ani- 
mal series,  how  the 
sex  organs,  espec- 
ially the  ovaries, 
are  developed  with- 
in the  body,  out  of 
harm's  way.  This 
protection  is  ex- 
tended to  the  em- 
bryo. 
How  much  more  alike  are  the  archegonia  of  bryophytes 
and  pteridophytes  than  any  other  parts  these  groups  possess ! 
Romanes'  classical  figures  of  vertebrate  ontogeny,  copied  on 
page  262,  show  how  much  more  alike  are  the  early  embryos 
of  vertebrates  than  any  of  their  subsequent  stages.  Where- 
fore our  systems  of  classification  of  organisms  have  tended 
to  be  based  more  and  more  on  developmental  phenom- 
ena. The  bipeds  and  quadrupeds  of  old  were  merged  as 
mammals,  animals  that  suckle  their  young;  and  the  pri- 
mary division  of  mammals  became  placentals  and  apla- 
centals — those  that  nourish  their  young  before  birth  through 
the  agency  of  a  placenta  and  those  which  do  not  so. 
Similar  illustrations  abound  in  all  the  higher  groups. 

Palaeontology  makes  known  to  us  the  life  of  past  ages,  by 
interpreting  such  fragments  of  organisms  as  have  actually 
come  down  to  us.  Embryology  furnishes  historical  data  of 
a  very  different  sort — not  the  organisms  of  the  past,  but  of 
the  processes  of  the  past,  in  so  far  as  preserved  in  the 


ORGANIC  EVOLUTION  261 

processes  of  the  making  of  the  organisms  of  the  present: 
not  armor  nor  bones  nor  any  other  finished  parts  of  organs, 
but  the  moulding  processes  of  the  basic  materials  out  of 
which  all  the  organs  are  formed.  In  these  processes  embry- 
ology gives  us  evanescent  glimpses  of  the  ground  lines  of 
phylogeny  in  so  far  as  they  are  preserved  in  the  successive 
stages  of  development  of  the  individual.  That  many 
features  of  all  embryos  are  ancestral  there  can  be  no  doubt. 
It  was  the  study  of  embryology  that  did  most  to  compel 
the  acceptance  of  the  doctrine  of  evolution  in  a  past  genera- 
tion. And  it  was  this  also  that  stimulated  to  greater  use 
of  the  historical  method  in  all  fields  of  investigation. 
Ontogeny  has  long  been  and  will  ever  be  one  of  the  most 
stimulating  fields  of  biological  investigation.  It  is  the  most 
synthetic  of  all.  In  the  bewildering  array  of  forms,  it  finds 
a  few  main  types  of  development,  themselves  traceable  to  a 
common  type  in  the  egg  cell.  And  it  shows,  withal,  how 
little  Nature  creates :  how  much  she  merely  transforms  and 
adapts. 

Study  J4.     The  ontogeny  of  organs  in  the  frog  or  salammider. 

Materials.  The  results  of  studies  25  to  28,  together  with 
whatever  additional  available  data  reference  works  may 
furnish,  supplemented  by  whatever  data  may  be  at  hand. 
Ecker's  Anatomy  of  the  frog,  and  Holmes,  The  Frog,  at 
least  should  be  available  for  reference. 

Tabulate  all  the  organs  that  show  marked  ontogenetic 
changes,  under  the  following  headings: 

I.  Organs  peculiar  to  developmental  stages  and  wanting 
in  adult. 

II.  Organs  functional  in  young,  vestigial  in  adult. 

III.  Organs  present  in  both,  but  serving  a  changed 
function  in  adult. 


262 


GENERAL  BIOLOGY 


Fig.    160.       Ontogeny  in  vertebrates  (after  Romanes). 


ORGANIC  EVOLUTION 


263 


IV.  Organs  developed  in  both,  but  better  developed  in 

adult. 

V.  Organs  rudimentary  or  absent  in  young,  and  func- 
tional only  in  adult. 

Progress  in  regres- 
sion.— There  is  an  im- 
portant sense  in  which 
all  regressive  develop- 
ment spells  progress. 
One  must  take  into  ac- 
count the  whole  man- 

%kl^  ^  ^         ^^^  ^^^  ^^  ^^^^  ^^  ^^^  organ- 

3^1  jj^  iJjiM^  ism  to  comprehend  this. 

^S^jT  ■\nS?"  Even  the  most  abject 

^       X    \^  ^      ^         parasite,    losing  all  or- 

_^  k  k  k^lK  gans    for    independent 

^7^"*^        V  ^NraQ^^  existence,  is  advancing 

in  its  own  peculiar  way 
of  getting  on  in  the 
world. 

There  is  also  a  sense 
in  which  regressive 
development  is  to  be 
considered  a  part  of 
the  normal  life  of 
an  individual.  As  nutritive  and  reproductive  functions 
come  successively  into  dominence  in  the  lifetime  of  every 
organism,  so  a  retrograde  development  of  nutritive  organs 
may  begin  with  the  taking  up  of  the  labor  of  reproduc- 
tion. This  is  well  illustrated  by  the  common  rag  weed. 
The  leaves  shown  in  figure  161  were  developed  at  differ- 
ent periods  of  the  life  of  a  single  plant.  They  are  divid- 
ed into  two  series,  which  parallel  the  wax  and  wane  of 
vegetative  vigor  in  the  plant.     The  second  series  is  the  one 


b 


Fig.  161.  Leaves  of  the  ragweed  {Ambrosia 
artemiscrfolia) .  a,  cotyledons;  b  to  e, 
leaves  successively  formed  in  youth,  ni, 
the  mature  leaf  form;  n  to  5,  the  dimin- 
ishing series  of  leaves  successively  formed 
during  the  period  of  seed  production;  z, 
a  fruiting  tip. 


264  GENERAL  BIOLOGY 

of  interest  here ;  it  begins  with  the  maximum  development 
in  size  and  complexity  of  leaves  at  sexual  maturity,  and, 
passing  through  a  diminishing  series,  ends  with  cessation 
of  leaf  production  when  all  the  energies  of  the  plant  are 
given  over  to  the  ripening  of  its  seeds. 

Why  evolutionary  series? — It  has  long  been  the  custom  of 
naturalists  to  arrange  organisms  in  series;  such  arrange- 
ment facilitates  dealing  with  large  numbers.  The  compara- 
tive anatomists  of  the  first  half  of  the  19th  century,  who  did 
so  much  to  advance  biological  knowledge,  believed  in  special 
creation,  and  in  the  fixity  of  the  species.  They  determined 
homologies  with  great  conscientiousness  and  arranged 
organisms  in  natural  groups;  but  for  them,  homology 
meant  likeness  in  structure  merely,  and  not  kinship,  and 
their  groups  were  "natural"  in  the  sense  that  like  had  been 
associated  with  like  in  them.  The  organisms  of  a  series 
were  no  more  related  to  each  other  than  a  series  of  one  type 
of  vessels  made  by  the  same  potter.  Why  then  do  we  con- 
sider that  natural  grouping  signifies  blood  relationship? 
Why  are  the  series  we  arrange  evolutionary  series  to  us? 

It  is  because  evolution  alone  affords  a  consistent 
and  satisfactory  explanation  of  the  facts  now  known  con- 
cerning the  structure,  the  development  and  the  past  history 
of  organisms.  The  student  who  has  done  the  work  hitherto 
outlined  will  have  felt  this  explanation.  But  perhaps  it 
may  not  be  amiss  to  briefly  indicate  at  this  point  a  few  classes 
of  facts  that  speak  especially  for  evolution,  and  that  seem  to 
stand  in  the  way  of  any  other  explanation : 

1.  The  plasticity  of  species  under  domestication,  and 

2.  The  intergradation  of  species  in  nature. 

Both  these  phenomena  are  well  enough  known  co  every 
observing  person  and  each  shows  that  species  are  not  fixed 
and  immutable.  The  individuals  of  a  species  may,  there- 
fore, be  arranged  in  a  series  with  its  extremes  having  very 


ORGANIC  EVOLUTION  265 

different  appearance,  and  the  differences  between  them 
may  sometimes  be  correlated  with  their  geographic  dis- 
tribution, and  sometimes  not. 

3.  The  close  adherence  to  structural  type  in  the  mem- 
bers of  a  single  group  that  is  modified  for  great  diversity  of 
habit  and  environment;  and,  conversely 

4.  The  superficial  similarity  wrought  in  different  struc- 
tural types,  when  they  are  modified  to  a  common  mode  of 
existence. 

5.  Correlations  of  structure ;  when  one  part  of  any  type 
is  modified  for  a  different  sort  of  life,  other  parts  are  modified 
in  harmony  therewith.  The  foot  a  of  figure  148  is  never 
associated  with  the  beak  b,  or  with  any  other  beak  in  the 
series,  except  with  beak  of  the  type  a.  This  is  the  sort  of 
concordance  that  makes  the  interpretations  of  fossil  frag- 
ments possible. 

6.  Vestigial  structures;  why  should  these  exist  at  all, 
except  they  be  ancestral? 

7.  The  tendency  of  all  embryos  to  recapitulate  group 
characters.  Why  should  such  a  tendency  exist,  but  for 
age-long  heredity? 

The  palaeontologic  record  is  exceedingly  fragmentary,  and 
especially  lacking  in  the  more  simple  forms,  that  would  be 
most  significant  to  us.  The  phylogenetic  record  is  broken 
by  the  absence  of  connecting  forms  between  the  groups, 
existing  organisms  being  only  the  twigs  of  branches  that  are 
often  widely  separated.  The  ontogenetic  record  is  perver- 
ted by  marked  departures  from  the  original  course  of 
development.  But,  notwithstanding  these  difficulties, 
which  are  so  great  as  to  make  it  easy  to  err  in  the  interpreta- 
tion of  nature's  genealogies,  the  evidence  of  descent  is 
thoroughly  convincing.  It  is  the  more  so  because  of  the 
w^ay  in  which  each  of  the  partial  records  supplements  and 
corroborates  the  others,  and  it  is  certainly  significant  that 


2  66  GENERAL  BIOLOGY     ' 

the  developmental  lines  traceable  backward  through  both 
ontogeny  and  phylogeny  are  all  convergent.  They  point  to 
a  common  origin  in  the  remote  past,  and  to  "descent  with 
modification." 

III.       THE  PROCESSES  OF     EVOLUTION;      ATTEMPTED 

EXPLANATIONS. 

Facts,  such  as  have  been  before  us  in  the  preceding  studies 
have  satisfied  biologists  generally  that  evolution  has  been 
the  method  of  nature;  but  the  theories  that  have  been 
advanced  in  explanation  of  the  processes  whereby  evolution 
has  been  wrought  out,  have  not  met  with  so  general  accept- 
ance. Yet,  if  evolution  has  had  a  past,  it  will  have  a 
future;  and  that  future  is  of  importance  to  us,  because  it 
must  include  the  destiny  of  all  races,  including  our  own. 
Nothing  could  be  of  more  practical  importance  to  us  than 
that  we  should  understand  the  conditions  of  evolutionary 
progress,  especially  if  these  conditions  should  prove  amen- 
able to  our  control. 

Many  explanations  have  been  offered,  and  some  of  them 
appear  in  part  really  to  explain.  All  of  them  are  under 
scrutiny  at  the  present  time.  Investigations  are  in  progress 
to  determine  their  validity.  It  is  well  to  reserve  judgment, 
but  it  is  also  well  to  know  the  main  features  of  the  current 
explanations;  for  such  knowledge  is  part  of  the  common 
intelligence.  Some  of  the  rnore  important  explanations 
will,  therefore,  be  outlined  briefly  here  and  in  the  next 
chapter. 

Natural  selection. — The  first  explanation  to  receive  any 
general  approval  (or  even  to  attract  much  notice)  was  that 
of  Charles  Darwin.  He  observed  how  breeders,  by  selecting 
and  isolating  new  forms  as  they  arise  in  domesticated  ani- 
mals and  plants,  are  able  to  establish  new  varieties  or 
races.     He  saw  them  producing  perfectly  definite  results; 


ORGANIC  EVOLUTION 


267 


horses  bred  for  draft  or  for  speed ;  peas  selected  for  color  of 
flower  or  for  palat ability  of  seed,  etc.  And  in  his  mind's 
eye  he  saw  nature  producing  like  results  by  the  removal  of 
the  unfit  and  the  preservation  of  those  best  suited  to  her 
conditions.     So,  he  called  the  process  natural  selection. 

The  theory  of  natural  selection  is  based  on  four  facts: 
i)  Organisms  vary;  2)  In  every  species  more  young  are 
produced  than  can  possibly  survive;    3)  Offspring  tend  to 


Fig.  162.     Three  sassafras  leaves  from  the  same  tree. 


resemble  parents ;  and  4)  There  exists  competition  between 
the  members  of  the  earth's  population. 

Inheritance  w411  be  considered  in  the  next  chapter.  Let 
us  here  examine  the  other  three  classes  of  facts  severally. 

Variation. — Animals  and  plants  vary.  No  two  persons 
look  alike,  nor  do  the  individuals  of  any  species,  on  suffi- 
ciently close  acquaintance.  The  careful  shepherd  knows 
his  sheep  as  individuals,  and  it  is  only  to  the  casual  observer 


2  68  GENERAL    BIOLOGY 

that  they  look  alike.  The  robins  on  the  lawn  may  be 
known  personally  by  any  one  who  will  take  the  trouble  to 
note  personal  characteristics. 

Nature  abounds  in  little  refinements  of  structure,  such  as 
we  see  in  the  raised  lines  traversing  the  cuticle  of  our  finger 
tips.  These  lines  are  never  exactly  alike  in  any  two  per- 
sons. So  distinct  are  these  differences  that  finger  prints  are 
now-a-days  a  well  recognized  aid  to  the  identification  of 
criminals.  No  two  leaves  on  any  tree  are  exactly  alike; 
indeed  those  on  the  same  tree  may  exhibit  differences  that 
are  very  marked  (fig.  162). 

Fluctuating  variations.  The  differences  between  the 
individuals  of  a  species  extend  to  every  personal  character- 
istic: stature,  strength,  activity,  temperament,  etc.,butthey 

are  usually  slight,  and  fluct- 
FiG.  163.    A  six-spined  seed    uatc   about    a    mean  that 

of  the  rag  weed.  , ,  i 

\  expresses  the  normal  con- 

dition for  the  species.  This  may  be  simply  illus- 
trated by  the  seeds  of  the  com.mon  rae  weed  (fig. 
163)  each  of  which  bears  a  long  apical  point,  sur- 
rounded by  a  circle  of  short  spines.  The  normal 
number  of  these  spines  appears  to  be  six,  but 
many  seeds  have  five  or  seven  of  these  spines,  and  a  few  have 
even  smaller  or  greater  numbers  of  them.  A  count  of  the 
spines  on  loo  seeds  taken  at  random  gives  the  following 
results: 

No.  of  spines  1234       5       6       7       89 

No.  of  times  occurring  i  3  7  9  25  37  25  12  i 
If  now  the  seeds  of  each  class  be  arranged  in  columns,  and 
aline  be  drawn  joining  the  tops  of  the  columns,  that  line  will 
be  the  curve  of  variation  (fig.  164),  a  common  means  of 
expressing  variations  of  this  type. 

The  class  containing  the  greatest  number  of  seeds  (called 
the  mode;    the  six  spined  class  in  this  case)  may  be  regarded 


OPGANIC  EVOLUTION 


269 


40 


36 


32 


28 


-4 


20 


lu 


12 


■-.Tipw^yjww^g; 


["■"g.'iaa 


^ 
^ 

^ 


^ 

^ 

A 

\ 

^ 

A 

-■^  ■ 

^ 

v\ 

^ 

^ 

^  \ 

V 

^ 

% 

^ 

\ 

^ 

% 

X 

\ 

■^ 

-^ 

> 

> 

^ 

*% 

>% 

A 

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— i 

Fig.   164.     One  hundred  rag  weed  seeds  arranged  in  classes   according    to  the 
number  of  their  spines.     The  Hne  represents  their  curve  of  variation. 


270 


GENERAL  BIOLOGY 


a 


o 


/ 


Fig.  165.  Leaves  of  the  smooth  sumac,  showing  variation,  a,  the 
normal  odd — pinnate  leaf;  h,  an  abrupt  pinnate  leaf;  c  and  d, 
intermediate  forms  (in  the  tabulation,  such  were  counted  for  the 
whole  number  to  which  they  most  nearly  approximated)  ;€,  an  odd- 
pinnate  leaf  with  a  leaflet  of  one  pair  omitted  (of  rare  and  prob- 
ably accidental  occurrence) ;  /  and  g,  leaves  from  the  base  of  the 
fungus  gall  that  is  shown  in  fig.  28,  page  37,  showing  a  tendency 
(under  the    stimulus  of    the  parasite),  to  be  more  compound. 


ORGAXIC  EVOLUTION 


27J 


as  representing  the  normal  condition  for  the  species.  It 
will  be  observed  that  the  variations  from  the  normal  are 
here  a  little  more  numerous  on  the  side  of  fewer  numbers  of 
spines,  but  that  the  curve  is  nearly  symmetrical.  It  is  an 
approximation  to  the  sym^metrical  mathematical  curve 
representing  the  distribution  of  error.  Chance  variations 
fluctuate  thus  about  the  normal. 

A  count  of  the  ray  flowers  of  315  heads  of  the  bur  mari- 
gold, gives,  when  the  results  are  plotted,  a  curve  that  is  very 
much  askew: 

No.  of  ray  flowers  (classes)  345     6     7       891011 

No.  times  occurring  (frequencies)  2  3819522219     o     i 


Fig.  166,     The  curve  of  numerical  variation  in  leaflets  of  the  smooth  sumac,  2730  leaves  counted. 


272  GENERAL    BIOLOGY 

The  normal  flowering  head  has  eight  ray  flowers,  and  the 
relatively  fewer  variants  are  nearly  all  on  the  side  of  the 
lesser  numbers. 

In  the  midst  of  such  fluctuating  variations  there  sometimes 
exists  a  marked  tendency  toward  a  definite  structural  type. 
Such  is  the  tendency  of  the  compound  leaves  of  the  smooth 
sumac  (fig.  165)  to  be  odd -pinnate;  that  is,  to  have  one 
terminal  unpaired  leaflet,  with  all  the  other  leaflets  arranged 
in  pairs.  A  count  of  the  leaflets  of  2  730  leaves  of  this  species 
results  as  follows: 

No.  of  leaflets  (classes)  56     7     8     9   10   11    12 

No.of  times  occurring  (frequencies)  3  9  24  11  57  20  75  30 
13  14  15  16  17  18  19  20  21  22  23  24  25  26 
224  71  352  80  501  106  331  35  143  14  31  4  7  2 
Here  is  a  total  of  1748  odd-pinnate  and  of  382  abrupt- 
pinnate  leaves.  The  broken  curve  which  these  figures 
yield  is  obviously  the  equivalent  of  two  similar  curves  for  the 
two  types  of  compound  leaf,  and  the  greater  height  of  the 
odd-pinnate  curve  is  the  index  of  the  tendency  toward  such 
leaf  type  in  this  species. 

Study  J5.      Fluctuating  numerical  variations. 

Select  some  common  organism  or  organ  having  parts  that 
can  readily  be  counted  and  that  vary  in  number,  and  study 
the  variation  in  numbers  of  these  parts.  Let  the  numbers 
be  small  ones  (for  economy  of  time  in  counting,  prefer- 
ably not  above  20).  Such  things  as  the  seed  spines,  ray 
flowers,  or  leaflets  of  a  compound  leaves  just  cited  in  these 
pages,  or  leg  spines,  wing  hooks,  leaf  lobes,  etc.,  etc.,  are 
everywhere  available  in  sufficient  abundance.  Gather  the 
material  at  random.  Count  at  least  100  specimens  and 
record  the  classes  and  the  number  of  times  occurring,  as 
in  the  first  example  cited  (see  fig.  164).  Then  plot  the 
curve  of  variation  on  a  square  of  cross-section  paper,  lay- 


ORGANIC   EVOLUTION 


273 


ing  off  the  classes-upon  the  ordinates  and  the  frequencies 

upon  the  abscissae. 

Then,  if  this  work  be  done  by   a  class,  let   the    totals 

of  all  the  individual 
counts  be  represented 
i  n  another  curve, 
plotted  in  another 
color  upon  the  same 
square;  this  will,  on 
account  of  the  greater 
numbers,  more  truly 
represent  the  normal 
variation  for  the 
species,  and  it  should 
be  a  closer  approxi- 
mation to  the  sym- 
metrical and  balanced 
curve  of  distribution 
of  error. 

The  record  of  this 
study  will  consist  in : 

i)  A  drawing  of  a 
variant  showing  the 
normal  condition  for 
the  species,  labelled 
with  the  name,  and 
showing  clearly  the 
parts  counted  and 
plotted. 

2)     The  individual  and  collective  curves  of  variation. 
Mutation. — Variations  are  not  all  so  Hght  and  inconstant. 
Figure  167  shows  a  variant  of  the  common  Hnaria  (L.  vul- 
garis, "butter  and  eggs"),  the  ordinary  flowers  of  which  are 


Fig.  167.       A  probable  mutant  of  Linaria  (L. 
vulgaris) ,  "butter-and-eggs." 


274 


GENERAL   BIOLOGY 


Fig.  168.     The  normal  flowers  of 
Linaria. 


shown  in  figure  1 68.     Among  the  offspring  of  a  single-spurred 

and  strongly  bilateral  flower 
appeared  this  one  plant  bearing 
mainly  five-spurred  and  radial 
flowers.  Such  larger  variations, 
when  they  affect  a  number  of 
correlated  characters  so  as  to 
change  the  aspect  of  the  organ- 
ism, and  when  with  self  fertiliza- 
tion they  are  self  maintaininc 
(i.  e.,  when  they  "breed  true"), 
are  known  as  mutations.  That 
mutants  establish  a  new  grade 
of  variations  is  evidenced  by  the 
fact  that  each  mutation  estab- 
lishes a  new  normal,  about 
which  ordinary  variations 
fluctuate. 
Mutations  appear  rather  rarely,  and  under  conditions 
that  are  not  at  present  understood.  Their  importance  as 
starting  points  in  the  development  of  new  races  of  plants  and 
animals  is  well  recognized  by  breeders.  The  long  and  care- 
ful pioneer  study  of  them  by  Hugo  DeVries  has  made  clear 
their  probable  importance  as  starting  points  in  the  evolution 
of  new  species.  DeVries  calls  many  of  the  mutants  he  has 
found  "elementary  species."  Their  significance  will  again 
be  referred  to  in  the  chapter  on  inheritance. 

More  young  produced  than  can  survive. — The  species  of 
organisms  differ  extraordinarily  in  the  number  of  young 
produced,  but  all  agree  in  the  tendency  to  increase  in  a 
geometric  ratio.  The  offspring  of  a  single  parent  may 
number  millions,  or  may  be  but  few;  but  in  either  case,  if 
all  survived  to  reproduce  in  like  ratio,  the  earth  would  soon 
lack  standing  room  for  the  progeny.     In  the  edge  of  the 


ORGANIC   EVOLUTION  275 

pond  a  single  female  frog  may  lay  300  eggs  on  a  spring 
morning,  and  she  may  repeat  the  performance  in  successive 
years.  If  half  of  the  succeeding  generations  were  females, 
and  were  at  maturity  equally  prolific,  and  if  all  should  sur- 
vive to  reproduce,  a  simple  calculation  would  show  that  in  a 
very  few  years  we  should  have  more  bulk  of  frogs  than  of 
water  in  the  pond.  Three  pairs  of  oftspring  in  one  hundred 
years  is  said  to  be  the  rate  of  reproduction  of  the  African  ele- 
phant—a rate  phenomenally  slow ;  yet  even  this  is  an  increase 
of  300%  in  a  century — sufficient  if  maintained  without  any 
losses  except  from  old  age,  to  cover  the  earth  with  elephants. 

It  is  by  excess  of  births  that  nature  provides  for  inevitable 
losses;  and  the  excess  is  proportioned  to  the  dangers  to  be 
encountered  in  the  race  of  life.  A  single  pike  may  lay 
upwards  of  80,000  eggs  each  season,  scattering  them  broad- 
cast in  shoal  waters,  where  most  of  them  early  fall  a  prey  to 
other  fishes.  When  hatched,  their  ranks  continue  to  be 
thinned,  however,  in  a  diminishing  ratio,  as  they  become 
larger  and  better  able  to  take  care  of  themselves.  But  if  out 
of  all  these  offspring  there  remains  at  maturity  for  every 
pair  of  old  pike  a  single  pair  of  young  ones  surviving  to  re- 
produce each  season  80,000  potential  offspring,  this  race  of 
fishes  is  holding  its  own;  the  natural  balance  is  maintained. 
For  more  than  this  proportion  to  survive  persistently  would 
disturb  that  balance,  by  depleting  the  numbers  of  other 
fishes  on  which  pike  feed.  A  sunfish  that  guards  its  eggs 
until  hatched,  need  not  produce  so  many  of  them.  But 
every  species,  in  order  to  avoid  extinction,  must  produce 
sufficient  excess  of  off'spring  to  make  good  the  inevitable  loss 
of  life  during  immaturity,  and  the  failures  of  adult  life. 

Competition. — For  want  of  food,  therefore,  and  often 
indeed  for  want  of  standing  room,  the  vast  majority  of 
organisms  born  into  the  world  are  foredoomed  to  perish 
before  reaching  maturity.     Yet  the  method  of  nature  is  not 


2  76  GENERAL  BIOLOGY 

more  harsh  than  that  we  pursue  in  making  a  flower  bed. 
For,  do  we  not  sow  the  seed  thickly,  to  insure  a  good  stand, 
and  then  thin  out  rigidly  after  germination?  Among  all 
organisms  the  vast  majority  of  offspring  are  swept  away  by 
casualties  against  which  they  have  no  power  to  cope;  by 
exposure  to  unwonted  conditions,  to  floods,  to  drouth,  to 
ruthless  enemies,  to  diseases,  etc.  Here  the  elimination  is 
wholesale  and  indiscriminate.  But  casualties  are  more  or 
less  local  and  occasional,  and  they  always  leave  an  excess  of 
young  to  be  eliminated  by  slower  methods  which  allow  some 
play  for  the  powers  or  merits  of  the  individual,  and,  there- 
fore, some  opportunity  for  competition. 

The  struggle  for  existence. — The  thinning  out  process 
inevitably  goes  forward,  but  it  is  no  longer  wholly  indis- 
criminate, for  individuals  vary.  Some  are  better  fitted 
than  others  to  meet  and  cope  with  the  perils  and  exigencies 
of  life.  If  these  be  physical  agencies,  some  are  better  able 
than  others  to  withstand  excess  of  heat  or  cold  or  drouth; 
if  enemies,  some  are  better  fitted  than  others  to  combat,  to  > 
escape  or  to  elude ;  if  competitors,  some  are  stronger  than 
others  and  better  able  to  seize  and  appropriate  to  themselves 
the  lion's  share  of  the  means  of  livelihood. 

If  we  did  not  thin  our  seedling  bed,  nature  would  thin  it 
for  us  by  the  slower,  but  not  less  certain  methods  of  com- 
petition; and  a  few  of  the  seedlings  of  stronger  growth, 
reaching  down  more  deeply  with  their  roots  to  the  food 
supply  in  the  soil  and  spreading  out  their  leaves  more  broadly 
to  the  sunlight  would  prove  the  better  able  to  maintain 
themselves. 

The  survival  of  the  fittest. — Herein  lies  the  efficient  prin- 
ciple of  natural  selection.  The  fittest  survive.  Not  in  the 
face  of  casualties;  for  these  sweep  out  of  existence  good,  bad 
and  indifferent  alike.  Not  in  the  face  of  insuperable  diffi- 
culties ;  the  best  seeds  may  fall  where  there  is  not  sufficient 


ORGANIC  EVOLUTION 


277 


depth  of  earth;  the  best  may  have  no  chance  of  Hving. 
And  not  in  times  and  situations  of  piping  peace  and  plenty, 
when  there  is  a  Hving  for  all,  and  even  weaklings  may  reach 


CHARLES   DARWIN 

(1809-1882) 

Prophet  of  evolution,  whose  theory  of  natural  selection 

was  founded  by  almost  unexampled  industry  and 

patient   endeavor;    author   of  "The  Origin  of 

Species,"  the  most  influential  book  of  the 

nineteenth  century. 

maturity.  But,  casualties  and  disasters  of  station  aside, 
and  giA^en  a  stress  of  competition  keen  enough  to  call  into 
requisition  all  the  powers  an  individual  may  possess,  the 
fittest  survive.  They  survive  to  perpetuate  their  powers 
in  their  descendents.     This  means  evolution. 


278  GENERAL   BIOLOGY 

Fitness. — Fitness  for  natural  selection  consists  in  two 
things  : 

i)  Ability  to  get  a  living  and  to  reach  maturity;  this  is 
provision  for  individual  needs. 

2)  Ability  to  leave  well  equipped  descendents  possessed 
of  like  good  qualities.  This  is  provision  for  the  future  of  the 
race.  It  is  not,  therefore,  the  superior  excellence  of  a  par- 
ticular organ,  but  the  balanced  excellence  of  the  organism 
as  a  whole  that  is  of  tieterminative  value.  Good  leg  muscles 
doubtless  make  for  speed;  but  speed  alone  will  not  avail  the 
hunted  hare,  if  it  have  not  also  endurance  and  instincts  of 
self  preservation.  "The  race  is  not  always  to  the  swift." 
And  all  these  will  be  of  no  moment  whatever  from  the  point 
of  view  of  evolution  if  it  leave  no  well  born  descendents.  For 
the  sterile  variety  "carries  its  own  death  warrant."  What 
has  a  chance  of  survival,  therefore,  under  the  most  rigid 
natural  selection,  will  depend  on  what  variation  of  the 
several  parts  of  the  body  appear,  and  in  what  combination. 

Study  j6.     The  struggle  for  existence  among  seedlings. 

This  study  is  one  that  requires  time,  and  observations  at 
repeated  intervals;  the  struggle  for  existence  is  not  a 
matter  of  laboratory  periods.  Seedling  plots  of  ground, 
thickly  sown  by  nature  to  annual  weeds  are  always  to  be 
found  in  the  corners  of  neglected  gardens,  by  roadsides 
and  in  fence  rows.  Other  plots  in  wet,  shaded  places  by 
streams  are  overgrown  annually  by  wild  touch-me-nots 
(Impatiens),  and  in  sunny  places  by  smartweeds  (Poly- 
gonum) .  If  for  want  of  time  this  study  be  deemed  unavail- 
able for  class  use,  it  may  be  carried  out  by  anyone  in  his 
home  garden. 

Select  a  plot  of  ground  a  few  feet  square,  more  or  less, 
free  from  rooted  perennials,  in  which  nature  has  sowed  the 
seed  of  annuals  and  where  the  seedlings  are  just  beginning  to 


ORGANIC  EVOLUTION  279 

crowd  one  another.  Stake  it  out  with  markers  at  the 
corners.  Count  the  seedlings  present  and  record  the  num- 
ber, and  note  any  peculiarities  in  their  distribution. 

After  allowing  time  for  growth  of  several  additional 
leaves  and  a  little  differentiation  in  size  among  the  seedlings, 
count  them  again,  this  time  in  three  classes,  small,  medium 
and  large,  and  record  the  numbers. 

Watch  now  the  intensification  of  the  struggle  for  existejice 
and  count  the  survivors  of  the  three  classes  at  longer  inter- 
vals through  the  season,  and  record  the  results.  Count  in 
the  end  the  individuals  that  are  able  to  mature  seed. 

Tabulate  the  results,  showing  what  proportion  of  each 
class  fruited. 

Calculate  the  area  that  would  have  been  required  if  all  the 
plants  that  germinated  from  seeds  had  attained  the  mini- 
mum fruiting  size ;  if  all  had  attained  the  maximum  size  of 
the  species. 

Artificial  selection. — Man  selects  the  variants  he  finds 
among  his  cultivated  species  of  animals  and  plants,  not  for 
the  good  of  the  species,  but  for  his  own  advantage.  He 
selects  com  for  the  starch  or  for  the  protein  content  of  the 
seeds.  He  selects  cattle  for  beef  or  for  milk  production. 
He  selects  fowls  for  egg  production  or  for  rapidity  of 
growth,  or  for  form  of  comb  and  wattles  (fig.  169)  or  for 
color  or  sheen  of  plumage  or  for  feathers  or  spurs  on 
the  feet;  and  pigeons  and  gold  fish  he  selects  mainly  for 
qualities  that  suit  his  fancy.  In  the  variability  of  living 
organisms  he  finds  resources,  the  value  of  which  he  is  only 
just  beginning  to  comprehend. 

But,  his  improved  varieties  are  all  weaklings,  incapable 
of  maintaining  themselves  in  competition  with  the  wild 
races  from  which  they  are  derived,  and  requiring  to  be  isola- 
ted and  cared  for,  in  order  that  the  values  for  which  they 
are  selected  may  be  realized.     High  bred  race  horses  are 


2  8o 


GENERAL  BIOLOGY 


a 


Plymouth  Rock 


Black  Minorca 


Brahma 


Hoiidan 


short-lived,    of     nervous 
temperament  and  of  weak 
constitution.     Abelleflower 
apple  is  a  beautiful,  fragrant 
and  luscious  fruit,  but  the 
tree  that  bears  it  is  quite 
incapable  of   entering  into 
open  competition  with  the 
worthless  wild  crab  apple. 
Nothing   could   be    more 
striking   in   illustration    of 
this  point  than  the  certainty 
with    which    wild     species 
crowd   out   the    cultivated 
ones  on  abandoned  farms. 
Lop-eared     rabbits,     and 
flightless  ducks,  and  udder- 
encumbered     cows,     and 
small-boned,  small-brained 
pigs,  and  hairless,  witless, 
barkless   and  tailless   dogs 
are  all  freaks,   and  nature 
will  have   none    of    them. 
Her  own  creations,    while 
often  far  more  curious  and 
extraordinary  than  any  of 
these,  differ  from  them  all 
in  the  one  essential  quality 
of  fitness. 

This  then,  in  brief,  is  the 
doctrine  of  natural  selec- 
tion, as  a  partial  explana- 
tion of  the  process  of  evo- 
lution.    Heritable      varia- 


FiG.    169.     standard  varieties  of 
chickens  (after  Rice). 


ORGANIC    EVOLUTION  281 

tions  of  whatever  sort  or  origin,  furnish  the  materials 
of  progress,  and  the  competition  of  life,  when  of  eliminative 
severity,  "selects"  the  fittest  variants  for  survival,  chiefly 
by  the  elimination  of  the  less  fit.  Real  selection  involves  a 
psychic  factor;  it  may  occur  if,  for  example,  birds  select  the 
most  luscious  wild  cherries  or  other  fruit,  whose  seeds  they 
carry  to  a  place  favorable  for  growth ;  or  if  insects  select  the 
showiest  of  the  flowers  whose  pollen  they  distribute. 

Natural  selection  is  thus  seen  to  be  an  explanation  of  the 
modus  operandi  of  those  extrinsic  forces  that  tend  to  make 
every  race  conform  to  conditions  of  environment.  With 
the  intrinsic  forces  of  the  living  organism,  it  can  only 
indirectly  deal.  Natural  selection  does  not,  therefore, 
account  for  the  origin  of  anything  new  among  organisms, 
but  only  for  the  preservation  of  such  new  things  as  are 
heritable,  advantageous  and  fit.  Nevertheless,  it  is  at  this 
day  the  one  process  of  evolution  whose  operations  are 
clearly  set  forth. 

Orthogenesis. — By  this  name  we  designate  a  racial  ten- 
dency toward  some  one  particular  line  of  development :  an 
innate  tendency,  uncontrolled  by  external  conditions. 
Such  racial  development  is  not  fortuitous,  but  in  a  single 
direction,  straight  ahead,  as  the  name  indicates.  But 
orthogenesis  is  not  an  explanation  of  a  process;  it  is  merely 
a  name  for  one. 

The  orthogenetic  tendency  is  manifest  in  its  incipiency 
when  a  group  of  organisms  tends  to  vary  strongly  in  the 
direction  of  some  one  particular  structural  type ;  when  the 
variations  are  not  promiscuous  (indeterminate)  but  show  a 
strongly  marked 'trend.  This  is  illustrated  by  the  inherent 
odd-pinnateness  of  the  compound  leaves  of  the  sumacs; 
and  equally  well  by  the  inherent  abrupt-pinnateness  of  che 
leaves  of  the  cassias  (partridge  pea,  etc.)  It  is  best  illus- 
trated by  the  actual  history  of  races  as  revealed  by  the  long 


2  82  GENERAL  BIOLOGY 

records  of  palaeontology.  Many  definite  lines  of  specializa- 
tion, manifestly  independent  of  environing  conditions,  are 
traceable  among  fossils,  and  some  of  these  lines  of  specializa- 
tion may  be  followed  out  to  their  final  end.  Useful  struc- 
tures, such  as  in  their  beginnings  natural  selection  might 
have  favored, have  been  developed  far  beyond  their  optimum, 
and  their  possessors  have  disappeared  from  the  earth. 
Famous  examples  are  the  sabre-toothed  tigers  and  the 
Irish  elk.  The  canine  teeth  of  the  sabre-toothed  tiger  were 
so  over  developed  as  to  be  useless,  their  tips  projecting  out- 
side the  mouth  when  opened;  and  the  antlers  of  the  Irish 
elk  attained  such  size  and  weight  as  to  be  a  very  great 
encumbrance.  Well  developed  canine  teeth  are  manifestly 
advantageous  for  tearing  prey,  and  all  carnivorous  mam- 
mals have  them;  and  strong  horns  for  meeting  rivals  in 
combat,  are  advantageous  too,  and  the  males  of  most  social 
ruminants  have  them ;  but  in  both  cases  the  good  thing  was 
overdone ;   specialization  far  outran  utility. 

We  need  not  go  so  far  afield  for  illustrations  of  develop- 
mental tendencies  that  have  exceeded  utilitarian  demands. 
The  studies  of  floral  structures  in  Chapter  I  should  have 
brought  us  into  contact  with  numerous  examples.  What 
possible  use  is  there  for  all  the  complicated  apparatus  of 
the  milkweed  or  the  orchis  flower?  or  for  all  the  arching, 
scalloping,  and  fringing  of  the  lips  of  a  mint  flower?  Clearly 
the  living  substance  has  inherent  powers  that  manifest  them- 
selves in  racial  tendencies,  independently  of  outward  mold- 
ing forces,  and  that  sometimes  are  not  amenable  thereto. 

We  may  perhaps  conceive  of  orthogenesis  as  a  manifesta- 
tion of  a  sort  of  developmental  inertia.  A  genetic  tendency, 
once  set  going,  tends  to  keep  going  in  a  straight  line.  How 
it  starts  we  do  not  know.  Natural  selection  may  have 
something  to  do  with  its  survival  in  the  beginning,  but 
evidently  cannot  stop  it  at  the  point  of  optimum  develop- 


ORGANIC  EVOLUTION  283 

ment,  for  we  must  always  remember  that  there  can  be  no 
selection  of  single  characters;  it  is  individuals  that  are 
selected,  with  whatever  combination  of  characters  they  may 
happen  to  be  endowed.  If  the  fittest  Irish  elk  had  ever 
antlers  of  increasing  size,  the  only  possible  curb  to  antler 
developm.ent  would  lie  in  the  extermination  of  the  line. 
Natural  selection  can  affect  an  organ  only  when  that  organ 
causes  such  manifest  unfitness  in  the  organism  as  is  incom- 
patible with  the  conditions  of  racial  existence. 

The  phenomena  of  orthogenesis  indicate  that  the  springs 
of  genetic  progress  lie  very  deep  and  that  we  must  look  for 
the  origin  of  species  in  the  origin  of  variations  and  of  develop- 
mental tendencies.  This  matter  will  be  considered  a  little 
further  in  the  next  chapter. 

Segregation. — The  breeder  of  plants  or  of  animals  isolates 
his  choice  varieties  (except  when  propagated  asexually)  in 
order  to  obviate  the  retrogression  that  would  inevitably 
result  from  intercrossing  with  inferior  varieties.  Biparental 
reproduction  necessitates  this.  Nature  also  segregates  her 
new  forms  miore  or  less  rigidly,  and  by  a  great  variety  of 
means,  among  which  may  be  mentioned  both  external  and 
internal  agencies. 

i)  Geographic  barriers. — Two  closely  allied  species, 
whose  differentiation  from  one  another  may  have  been 
comparatively  recent,  are  often  found  on  opposite  sides  ot  a 
mountain  chain  or  desert,  or  other  impassible  barrier. 
Thus  most  of  the  fishes  found  on  the  two  sides  of  the  Isthmus 
of  Panama  are  represented  by  two  closely  allied  species,  one 
on  one  side  and  the  other  on  the  other  side.  This  is  held  to 
confirm  the  opinion  of  geologists,  that  the  two  oceans  were 
once  connected  across  the  isthmus  by  open  sea,  the  assump- 
tion being  that  time  enough  has  elapsed  since  the  emer- 
gence of  the  Isthmus,  closing  the  passage,  for  the  differentia- 


284 


GENERAL  BIOLOGY 


tion  of  the   species   from  each  other  and   from  the   com- 


mon original  stock. 


Fig.  170.  Diagram  of  the  distribution  of  the  common 
song  sparrows  of  North  America.  Shaded  areas  in- 
dicate the  range,  a  of  the  eastern  song  sparrow;  b,  of 
the  Rocky  Mountain  song  sparrow;  c,  of  the  gray 
song  sparrow;  d,  of  Samuel's  song  sparrow;  e,  of  Heer- 
mann's  song  sparrow;  /,  of  the  Oregon  song  sparrow, 
and  g,  of  the  rusty  song  sparrow. 


This  is  segrega- 
tion of  the  most 
obvious  sort. 
Many  a  wide 
ranging  species 
has  varieties  or 
sub-species  for 
every  distinct 
f  aunal  area  with- 
in its  range. 
The  accompany- 
ing map  illus- 
trates the  geo- 
graphic distri- 
bution of  the 
races  of  the 
common     song 


sparrow. 

AVhate\'er  the  means  employed,  nature  has  practiced 
segregation  on  a  large  scale,  even  isolating  more  or  less  the 
larger  groups  of  organisms — the  palms  in  the  tropics  of 
the  world,  the  marsupials  in  the  Australian  region,  etc.,  etc. 
This  is  a  subject  of  great  biological  interest  and  importance, 
but  it  falls  outside  the  scope  of  our  practical  studies  and 
therefore,  the  sttident;  is  referred  for  fuller  statement  to 
general  works  on  the  geographic  distribution  of  plants  and 
animals. 

2)  Climatic  and  meteorological  conditions. — Tempera- 
ture and  altitude,  rainfall  and  winds,  and  other  similar 
influences  differentiate  desert  and  plain,  meadow  and 
forest,  and  all  the  host  of  animal  and  plant  forms  that  accom- 
pany them.     This  is  so  familiar  a  matter,  that  any  one  who 


ORGANIC  EVOLUTION 


285 


has  travelled  a  few  hundred  miles  away  from  home  should 
be  able  to  illustrate  it  by  recalling  the  new  form  of  animals 
and  plants  met  with  in  the  new  environments  visited. 

3)  Physiographic  barriers. — We  often  find  two  closely 
allied  species  in  one  locality  inhabiting  haunts  that  are  just 
a  little  different  topographically.  This  is  illustrated  by  two 
of  our  common  dragon  flies,  one  of  w^hich  (Libellula  semi- 
fasciata)  inhabits  the  small  brooks  and  the  other  (L.  pul- 


FiG.    171.       A  common   pond    inhabiting    dragonfly    (Libellula 
pulchella). 

chella,  fig.  171)  the  small  ponds  over  a  considerable  part 
of  the  United  States.  This  matter  will  be  abundantly 
illustrated  in  Chapter  VI  under  the  subject  of  the  adjust- 
ment of  organisms  in  place. 

4)  By  ecological  differences. — Two  species  may  live  even 
nearer  to  each  other  and  yet  dwell  apart ;  as  in  the  case  of 
two  species  of  squirrels  of  the  same  locality,  one  of  which 
burrows  in  the  ground,  while  the  other  lives  and  nests  in 
trees.  This  sort  of  adjustment  in  place  also  will  be  studied 
in  Chapter  VI. 


286  GENERAL  BIOLOGY 

5)  A  species  might  segregate  itself  into  two  groups,  if 
among  its  members  there  should  arise  marked  differences  as 
to  the  date  of  the  breeding  season.  Those  maturing  early 
could  only  mate  with  others  of  like  early  development,  and 
would  thus  be  segregated,  '(permanently,  if  this  seasonal 
habit  were  heritable)  from  those  that  mature  late.  Differ- 
ences like  this  would  be  likely  to  be  correlated  with  other 
differences,  and  thus  two  races  might  begin  to  diverge. 

6)  A  species  might  be  segregated  into  two,  if  two  of  its 
groups  of  variants  should  be  mutually  sterile.  Such  variants 
occur  among  cultivated  species. 

7)  Two  races  are  developed  out  of  one  species  when  the 
variants  fall  apart  in  two  groups,  keep,  together  in  these 
groups,  develop  a  "race  feeling,"  and  refuse  to  interbreed. 
This  is  reported  to  have  occurred  not  infrequently  when 
considerable  numbers  of  deer  have  been  kept  in  private 
parks.  Birds  of  a  feather  flock  together,  even  when  the 
feather  is  distinctive  only  of  a  race  or  a  sub-species.  This  is 
the  kind  of  segregation  known  as  "preferential  mating.'" 

These  are  the  principal  means  whereby  nature  keeps  her 
creatures  apart  in  separate  strains,  or  in  groups  of  higher 
rank;  far  apart  if  the  barriers  be  external  agencies  of  isola- 
tion, but  still  apart  even  though  near  together,  if  there  be 
such  internal  agencies  as  prevent  intercrossing. 

The  interaction  of  external  and  internal  forces. — So  there 
have  been  and  are  still  two  main  types  of  explanation  of  the 
process  of  evolution,  typified  by  natural  selection  and 
orthogenesis;  the  one  emphasizing  outward  conditions,  the 
other,  inner  tendencies.  The  contemplation  of  the  environ- 
ment, and  of  the  fitness  of  organisms  thereto,  leads  to  the 
over  emphasis  of  adaptation;  the  study  of  the  spontaneous 
and  automatic  activities  of  the  living  substance,  tends 
toward  confidence  in  their  sufficiency.  The  two  have  much 
too  often  been  treated  as  though  they  were  mutually  ex- 
clusive. 


ORGANIC  EVOLUTION  287 

Direct  adapta  tion  seems  especially  to  explain  such  classics 
of  facts  as  are  furnished  by  geographic  distribution,  especially 
of  island  life,  by  parallelisms,  by  mimicry,  by  degeneration, 
etc.  Let  us  illustrate  by  means  of  the  parallelism  of  the 
swift  and  the  swallow.  How  have  these  birds  that  are  so 
different  structurally,  become  so  very  much  alike  in  form,  in 
flight,  and  in  foraging  habits  that  it  requires  something  of 
an  ornithologist  to  distinguish  between  them?  It  is  a 
peculiar  field  for  bird  life  that  they  occupy.  Above  the 
ponds  and  lakes  there  hovers  a  teeming  population  of 
midges  and  other  little  insects  excellent  for  food.  How 
have  these  two,  of  all  the  groups  of  birds,  become  so  finely  and 
so  similarly  fitted  to  profit  by  it?  Is  it  more  likely  that 
internal  forces  automatically  produced  such  external  like- 
ness built  upon  persistent  structural  unlikeness,  or  that  a 
common  environment,  imposing  common  conditions,  has, 
acting  through  long  ages,  shaped  to  common  form  and 
fimction  those  parts  with  which  it  came  most  directly  in 
contact?  When  Vv^e  note  the  numerous  details  of  similarity 
that  are  coupled  with  convincing  evidence  of  diverse  origin, 
we  incline  to  doubt  that  these  likenesses  can  be  wholly  due 
to  internal  spontaneous  developmental  tendencies,  just  as 
we  doubt  the  originality  of  two  essays  that  show  many 
points  of  correspondence.  Surely  internal  forces  would 
modify  internal  form,  as  well  as  external.  The  impress  of 
environment  appears  in  this  that  it  is  the  outside  of  organ- 
isms that  show  all  the  special  fitnesses  to  the  environing 
conditions.  As  a  distinguished  American  zoologist  has 
graphically  stated  it,  "The  inside  of  an  animal  shows  what 
it  is;  the  outside  shows  where  it  has  been." 

Environmental  influence  comes  out  most  conspicuously 
where  different  environm.ents  impose  very  different  condi- 
tions; as,  for  example,  Avhen  part  of  a  group  passes  over 
from  terrestrial  to  aerial  or  to  aquatic  life.  Some  such  cases 
will  be  taken  up  for  special  study  in  Chapter  VI. 


2  88  GENERAL  BIOLOGY 

Nature  has  set  bounds  to  which  all  the  Hving  must  con- 
form themselves.  This  is  seen  not  alone  in  externals  of  form, 
l3Ut  also  in  the  very  fundamentals  of  organization.  Even 
the  types  of  animal  symmetry  correspond  to  evironment. 
Of  the  three  main  types,  spherical  symmetry,  like  that  of 
volvox  (symmetry  about  a  point)  prevails  where  uniform 
conditions  exist  on  all  sides  of  an  organism;  radial  symme- 
try like  that  of  hydra  and  most  plants  (symmetry  about  a  line) 
prevails  when  conditions  are  alike  at  the  sides  of  the  axis  of 
the  body  but  differ  at  the  two  ends;  and  bilateral  symmetry 
like  that  of  the  higher  animals  (symmetry  about  a  plane), 
prevails  when  conditions  are  alike  upon  tAvo  sides  but  differ- 
ent above  and  below  as  well  as  before  and  behind,  as  they 
must  be  in  all  organisms  that  travel  over  the  surface  of  solids. 

On  the  other  hand,  there  are  phenomena  of  divergent 
development,  of  the  persistence  of  types  through  the 
vicissitudes  of  all  environmental  changes,  of  grotesqueries  of 
form,  and  superfluities  of  structure  and  ornamentation,  that 
speak  most  strongly  for  the  dominance  of  the  inner  forces  of 
life,  and  that  negative  or  minimize  external  influences. 

But  it  is  not  wise  to  exclude  the  possible  action  of  either 
inward  or  outward  forces  in  development  when  we  know 
that  both  are  ever  present.  The  sightless  condition  of  the 
fishes  that  live  in  the  underground  streams  of  caves  in  total 
darkness  has  often  been  treated  as  though  it  were  a  case  of 
pure  adaptation.  But  when  we  note  that  other  fishes 
belonging  to  the  same  family  (Amblyopsid  ae)  have  weak 
eyes  and  incline  to  stay  in  the  deeper  shadows  of  the  shores, 
we  see  that  a  racial  tendency  toAvard  this  sort  of  develops 
ment  may  have  favored  the  adaptation.  Nature  may  have 
segregated  the  fishes  best  suited  to  cave  life  in  the  environ- 
ment  best  suited  to  them,  and  then  may  have  gone  on  per- 
fecting  the  adaptation,  either  directly,  or  by  perfecting  the 
tendency,  or  by  both  means  concurrently.  Inherent  ten- 
dencies and  environmental  influences  are  ever  present,  and 
development  can  only  be  the  resultant  of  their  interaction. 


CHAPTER  IV. 
INHERITANCE. 

Nothing  is  more  familiar  than  the  close  adherence  of 
offspring  to  the  specific  type  of  their  ancestry.  Although 
variations  abound,  they  occur  within  very  narrow  limits. 
The  egg  of  a  frog  can  produce  only  a  frog;  never  a  newt,  or  a 
salamander.  A  hen  sitting  on  duck's  eggs  can  never  avail 
to  hatch  an3^hing  but  ducklings  out  of  them;  for  there  is 
nothing  else  in  them.  Moreover,  our  confident  expectation 
that  offspring  will  resemble  not  only  their  race,  but  their 
individual  ancestors  as  well  is  expressed  by  the  proverb, 
"Like  father,    like  son." 

Heredity  and  variation  are  two  aspects  of  evolution  as 
viewed  from  the  standpoint  of  the  present,  heredity  looking 
toward  the  past,  and  variation  toward  the  future.  But 
whether  a  valuable  variation  counts  for  anything  or  not  in 
racial  development  depends,  as  we  have  seen,  upon  whether 
it  is  heritable  or  not.  Hence  we  must  ask,  whether  able  to 
answer  or  not,  what  is  the  nature  of  the  bond  between  the 
generations  ?  Such  facts  as  have  been  accumulated  bearing 
on  this  question  may  be  briefly  considered  under  two  heads: 
i)  the  visible  mechanism,  and  2)  the  observable  results  of 
heredity. 

I.        THE    VISIBLE    MECHANISM    OF    HEREDITY. 

The  process  of  reproduction  is  one  of  the  chief  distinguish- 
ing phenomena  of  living  things.  We  have  in  the  preceding 
pages  considered  numerous  remarkable  structures  and 
developments  connected  with  it.  But  to  distinguish  its 
essentials  Ave  must  now  retrace  our  steps  and  consider  again 
the  simpler  organisms.  The  yolk  accumulation,  the  em- 
bryonic membranes,  the  milk  glands,  etc.,  which  we  have 


290  GENERAL  BIOLOGY 

been  considering  are  mere  accessories  of  birth  and  being. 
Even  the  primitive  vertebrates  lack  them  all;  they  have 
only  eggs  and  sperms,  and  often  merely  scatter  these  free  in 

the  water,  to  develop 

Fig.    173.       Diagram   of  the  division       -rTr-i-fVi/-.ii+      -fn-H-Vio-r      t^o 
of  a  paramoecium  (after  Jennings).       ^itnOUt      turthcr      pa- 

a  and  6  show  loss  of  specific  Charac-  -ro-n-l-ol      r^r\r,  +  r,r^+      r^r-     i-r-> 

ters;  c,  d  and  e  show  division;  /,  g       renxai    COntaCt    Or    m- 
and  h  show  re-formation  of  one  of       ft^^(2,■nnf^        a  n  /\     tttV.  oti 

the  daughter  cells.  nucncc,    ano    wncn 

we  reach  the  simplest 
organisms,  in  some  of  them  we  find  not  even  sex  cells 
but  only  protoplasm ;  yet  there  appears  to  be  faith- 
ful reproduction  of  parental  characters;  and  again 
we  are  impressed  with  the  fact  that  the  primary 
functions  of  life  are  functions  of  protoplasm. 

In  chapter  II  we  traced  the  origin  of  separate 
germ  cells.  Let  us  now  note  certain  fundamental 
likenesses  and  differences  of  development  with  them 
and  without  them.  First,  there  is  continuity  of 
living  substance  in  either  case.  A  part  of  the  old 
lives  on  in  the  new.  The  protoplasm  out  of  which 
new  organisms  are  formxcd  is  potentially  immortal. 
Secondly,  reproduction  is,  to  a  greater  or  less  extent, 
a  new  production  in  either  case.  Even  the  two 
daughter  cells  of  a  protozoan  are  not  merely  halves 
of  a  divided  mother  cell ;  for  the  materials  of  that 
cell  have  been  reformed  with  more  or  less  of  change. 
The  unicellular  organism  undergoes  regressive 
change  before  division  takes  place;  the  specific 
characters  are  lost,  to  be  refashioned  during  the 
adolescence  of  the  new  cell  (fig.  173).  The  process 
has  been  aptly  likened  by  analogy  to  the  dissolving 
of  a  crystal  in  its  mother  liquor,  to  be  subsequently 
recrystallized  out  of  it. 

On  the  other  hand  there  are  very  considerable  differences, 
accompanying  development  by  means  of  germ  cells.     These 


INHERITANCE  291 

alone  have  descendents  living  on  in  successive  generations. 
Being  protected  within  the  body  of  a  multicellular  organism 
and  having  no  nutritive  functions  to  perform,  they  are 
removed  from  direct  contact  with  environment,  and  remain 
unspecialized  with  reference  thereto.  The  germ  cells  are 
developed  from  the  egg  along  with  the  body  cells,  but  are  set 
apart  therefrom,  sooner  or  later  in  the  course  of  differentia- 
tion. Soon  the  body  cells  invest  the  germ  cells  with  a  cover- 
ing in  which  they  are  sheltered  and  nourished  during  all 
their  subsequent  development.  This  general  relation 
between  germ  plasm  and  body  plasm  is  diagrammatically 
set  forth  in  figure  174. 


Fig.  174.  Diagram  of  the  relation  between  germ  plasm  and 
body  plasm.  5,  body  plasm  (soma),  egg  and  sperm  shown 
below,  and  zygote  (circle  inclosing  dot)  beyond;  s,  s,  s,  the  line 
of  succession;  i,  the  line  of  descent. 

It  may  well  be,  therefore,  that  parent  and  offspring 
resemble  each  other  because  both  are  developed  from  the 
same  stock  of  germ  plasm. 

Every  organism  begins  life  as  a  single  cell.  It  behooves 
us,  therefore,  to  look  a  little  more  closely  into  the  structure 
of  the  cell.  Since  the  fertilized  egg  may  develop  into  the 
complete  individual  without  further  parental  influence,  that 
new  individual  must  be  potentially  present,  and  also  the 
mechanism  whereby  its  parts  are  wrought  out.  To  the  egg 
cell  let  us  go,  therefore,  to  learn  further  of  the  nature  of  this 
mechanism.  Our  task  will  be  easier  if  we  examine  the 
minute  transparent,  nearly  yolkless  eggs  of  such  simple 
marine  organisms  as  sea  urchins  and  starfishes,  which  if 
placed  alive  in  sea  water  under  the  microscope  will  go  on 
developing,  the  divisions  succeeding  each  other  in  quick 


<n 


292 


GENERAL  BIOLOGY 


pT^p0 


Fig.  175.  Diagram  of  nuclear  behavior  in  cell  division  (after 
Wilson),  a,  resting  stage  between  divisions;  h,  beginning  of 
division  phenomena;  c  and  d,  formation  of  nuclear  spindle 
and  fragmentation  and  splitting  of  chromosomes;  e  tof,  later 
stages:  t,  centrosomes;  u,  nucleolus;  v,  spireme;  w,  chromo- 
somes; or,  a::,  asters:  y,  chromosomes  in  equatorial  plate;  z, 
chromosomes  separating. 


INHERITANCE  293 

succession  before  our  eyes.  Nothing  could  be  more  convinc- 
ing of  the  wonderful  refinement  of  structure  of  the  living 
substance,  or  of  the  precision  of  its  processes,  than  to  watch 
the  behavior  of  the  nucleus  in  a  segmenting  egg.  And  if  we 
supplement  what  we  can  see  in  life  by  an  examination  of  eggs 
that  have  been  fixed  at  different  stages,  and  stained  by  the 
precise  differential  methods  of  histology,  we  may  discover 
the  chief  phenomena  of  nuclear  behavior  that  regularly 
recur  at  every  cell  division. 

Figure  1 7  5  is  a  diagram  of  ordinary  (indirect)  cell  division. 
In  the  resting  stage  preceding  division  (a)  the  nucleus,  in- 
closed by  a  nuclear  membrane  is  seen  to  contain  an  irregu- 
larly disposed  darker  substance  (deeply  stained  in  his- 
tological preparations)  called  chromatin.  This  is  deposited 
in  a  network  of  excessively  fine  and  almost  invisible  threads 
of  a  substance  called  linin.  Besides  these,  the  watery  fluid 
in  which  these  lie  ("nuclear  sap")  there  is  also  present,  more 
or  less  constantly  a  rounded  body,  the  nucleolus,  different  in 
character  from  chromatin,  as  shown  by  its  staining  reactions. 
Outside  of  the  nucleus  but  lying  close  to  it  is  a  minute  body, 
the  centrosome. 

The  first  sign  of  division  appears  in  the  division  of  the 
centrosome ;  the  resulting  daughter  centrosomes  move  apart 
along  the  outside  of  the  nuclear  wall.  The  chromatin  inside 
that  wall  begins  to  be  gathered  together  in  a  long  convoluted 
skein  called  the  spireme  (h).  Before  the  centrosomes  reach 
opposite  sides  of  the  nucleus,  the  nuclear  wall  begins  to  be 
dissolved.  The  linin  threads  take  up  a  position  stretched 
between  the  two  centrosomes  and  so  form  the  nuclear 
spindle.  Corresponding  linin  threads  in  the  cytoplasm 
become  radiately  arranged  about  the  centrosomes  to  form 
the  two  asters.  The  chromatin  of  the  spireme  becomes 
broken  into  segments,  that  are  at  first  irregularly  disposed 
on  the  linin  threads,  and  that  later  are  shifted  to  the  middle 


294 


GENERAL    BIOLOGY 


of  the  spindle,  as  soon  as  the  spindle  is  fully  formed.  These 
are  called  chromosomes.  This  completes  the  first  phase 
(prophase)  of  division. 

Then  the  chromosomes  that  have  split  lengthwise,  each 
into  two  equal  parts,  move  apart  in  halves  along  the  lines  of 
the  spindle  in  two  equivalent  groups.  The  centrosome  also 
divides.  This  is  the  second  phase  {metaphase)  and  climax 
of  cell  division.  Now  there  is  provided  the  nuclear  material 
for  two  daughter  cells. 

The  two  succeeding 
phases  are  the  reverse 
of  the  first  two  phases. 
The  chromosomes 
move  in  the  next  phase 
(anaphase)  of  division 
to  the  ends  of  the 
spindle,  and  form  two 
compact  groups,which 
tend  to  coalesce  more 
or  less  into  a  spireme, 
and  a  nuclear  wall 
begins  to  be  devel- 
oped about  them  and 
the  spindle  begins  to  disappear.  Finally,  (telophase  of 
division)  the  chromatin  becomes  scattered  again  upon  the 
finer  mesh  work  of  the  dispersed  linin  threads,  the  cell  body 
divides,  and  the  resting  stage  with  which  we  began,  is 
resumed.  The  outcome  of  these  processes  is  that  each 
daughter  nucleus  receives  half  of  the  nuclear  material  of  the 
mother  cell.  However,  unequally  the  cell  body  may  be 
divided,  this  process  guarantees  an  equitable  distribution  of 
the  chromosomes  in  cell  descent. 

This  is  the  ordinary  indirect  process  of  nuclear  division 
known  as  mitosis  (or  karyokinesis) .     The  figures  successively 


Fig.  176.  Cell  division  in  growing  tissue  (sala- 
mander epidermis).  A  number  of  resting 
nuclei,  and  three  in  process  of  dividing,  a, 
spireme;  b,  anaphase  of  division,  and  c,  late 
anaphase. 


INHERITANCE  295 

formed  by  chromosomes,  aster  and  spindle,  are  known  as 
mitotic  figures.  These  regularly  appear  at  every  cell  divi- 
sion, not  only  in  the  embryo,  but  in  almost  every  growing 
part  of  the  body,  throughout  the  life  of  the  organisms. 
They  are  freely  exposed  to  view  in  living  transparent  eggs, 
but  in  any  developing  tissue  properly  sectioned  and  stained, 
nuclei  maybe  seen  in  some  of  the  division  phases  above  out- 
lined (fig.  176).  These  phases  follow  one  another  in  an 
inviolable  order;  each  stage  conditions  the  one  that  is  to 
follow  it;  and  together  they  seem  admirably  fitted  for  the 
equivalent  distribution  of  those  parts  of  the  nucleus  which 
appear  most  constant. 

What  role  these  parts  may  play  in  inheritance  it  is  as  yet 
impossible  to  say.  They  are  all  minute,  and  their  study  is 
attended  with  very  great  difficulty.  The  centrosome  is 
usually  at  the  limit  of  vision  with  the  best  microscopes,  and, 
hardly  anything  is  known  of  its  structure.  The  chromoso- 
mes are  the  nuclear  organs  most  readily  followed,  and  as  we 
have  just  seen,  between  spireme  and  spireme  these  are  scat- 
tered in  granules  on  an  inconstant  linin  mesh  work,  to  be 
reintegrated  at  each  successive  division.  Only  their  con- 
stituent chromatin  persists  in  our  view,  and  this  in  particles 
of  such  minuteness  as  to  be  individually  unrecognizable. 
Yet  the  chromosomes,  as  integrates  of  such  particles,  show 
such  constant  features  that  we  are  compelled  to  attribute 
considerable  importance  to  them.  They  appear  and  reap- 
pear in  like  number  and  in  similar  form.  The  number  dif- 
fers in  different  groups  but  it  is  constant  and  characteristic 
for  all  the  individuals  of  any  given  species,  in  all  the  cells 
of  the  body.  The  number  varies  from  2  in  a  species  of 
round  worm  (Ascaris)  to  168  in  the  crustacean  Artemia, 
ranging  in  most  ca.ses  between  12  and  36.  The  number 
appears  to  be  a  family  characteristic  in  the  grasshoppers,  it 
being  22  in  the  shorthorned  grasshoppers  and  33  in  the 
meadow  grasshoppers. 


296  GENERAL  BIOLOGY 

Chromosomes  exhibit  marked  individuality  of  form,  dif- 
fering in  different  organisms  in  length,  breadth,  curvature, 
etc.,  but  in  a  given  species,  they  are  fairly  constant  in  form. 
In  certain  genera  it  is  claimed  that  two  species  may  be  dis- 
tinguished as  well  by  the  chromosomes  of  a  single  cell*  as 
by  the  external  characters  of  the  adult  animal. 

The  history  of  the  germ  cells. — Since  at  the  beginning  of 
embryonic  life,  the  egg  is  already  a  new  organism,  charged 
with  the  potentiality  to  develop  all  the  characters  of  the 
adult,  we  must  seek  the  source  of  these  characters  farther 
back.  How  does  the  egg  come  into  being?  It  traces  its 
lineage  from  an  antecedent  egg,  as  we  have  already  seen  (fig. 
174).  That  antecedent  egg  gives  rise  to  both  body-plasm 
and  germ-plasm,  but  the  latter  is  very  early  set  apart  from, 
although  surrounded  by  the  former;  w^alls  are  built  up 
about  the  germ  plasm  (spermary  or  ovary  walls) ,  by  which 
it  is  protected  and  through  which  it  is  nourished.  Thus,  the 
germ  plasm  is  removed  from  direct  contact  with  environ- 
ment, and  also  from  direct  relations  with  the  functional  cells 
of  the  body,  and  in  this  isolation  it  develops. 

The  primordial  germ  cells,  thus  segregated,  pass  through  a 
period  of  rapid  divisions  which  succeed  each  other  in  quick 
succession  without  much  intervening  growth,  and  the  result 
of  which  is  great  increase  in  numbers  and  great  reduction  in 
size.  The  small  germ  cells  thus  produced  are  called  sperma- 
togones or  oogones,  according  as  they  develop  in  spermary 
or  ovary.  Then  follows  a  growth  period,  without  division, 
in  which  the  normal  size  is  regained,  and  much  new  cyto- 
plasm is  formed.  The  differentiation  of  the  cytoplasm  into 
the  different  materials  that  will  subsequently  be  devoted  to 
the  production  of  different  parts  of  the  embryo  occurs  dur- 


*They  differ  among  themselves  in  size  and  form  in  the  single 
nucleus;  wherefore,  it  is  ordinarily  the  chromosome  complex  that 
offers  recognition   characters,  rather  than  single  chromosomes. 


INHERITANCE 


297 


sperm\         ^    egg 

\  / 

z 


\  \  I  I 


pb 


Pig.  177.  Diagram  of  the  derivation 
of  the  sex  cells  (after  Boveri).  z, 
the  fertilized  egg  (zygote) ;  som, 
the  body  plasm  (soma);  t,  the  de- 
velopmental period  during  which 
the  germ  plasm  and  the  body  plasm 
are  indistinguishable;  sp,  sperm- 
ary;  ov,  ovary;  p,  primordial  germ 
ceils;  M,  the  period  of  rapid  in- 
crease in  number  and  diminution 
in  size  (the  number  of  divisions  is 
much  greater  than  shown) ;  v,  the 
period  of  increase  in  size  with  dif- 
ferentiation of  cytoplasm;  w,  the 
two  maturation  divisions ;  pb,  polar 
bodies;  e,  egg. 


ing  this  period.  Then  follows 
a  period  of  maturation,  or 
ripening  of  the  sex  cells,  which 
involves  two  successive  divi- 
sions only,  and  during  which 
the  germ  cells  are  known  as 
spermatocytes  or  oocytes. 
The  four  cells  resulting  from 
these  two  divisions  become 
the  sex  cells,  eggs  or  sperms, 
but  there  is  one  marked  differ- 
ence, indicated  in  the  accom- 
panying diagram  (fig.  177). 
In  the  case  of  spermatocytes, 
the  divisions  are  equal,  and 
four  sperms  result ;  but  in  the 
case  of  the  oocytes,  the  divi- 
sions while  equal  with  respect 
to  nuclear  parts,  are  very  un- 
equal with  respect  to  cyto- 
plasm,one  cell  retaining  nearly 
all  of  it,  the  others  being  cast 
out  from  it  as  the  so-called 
polar  bodies;  therefore,  but 
one  functional  and  perfect  Qgg 
results. 

Such  are  the  form  changes 
undergone  by  the  germ  cells 
during  their  development, 
among  the  higher  animals  in 
which  they  have  been  most 
carefully  studied.  They  are 
not  to  be  considered  as  occur- 
ring at  one  time  only  and  in  a 


298 


GENERAL  BIOLOGY 


direct  succession,  for  many  of  the  primary  germ  cells  remain 
undeveloped  through  the  life  of  the  individual  organism,  and 
in  most  organisms  they  develop  in  cycles,  corresponding  to 


ANTONY   VAN    LEEUWENHOEK 

(1632-1723) 

Pioneer  microscopist  and  naturalist;  maker  of  his  own 

lenses;  discoverer  of  capillary  circulation,  of 

sperm  ceils,  etc. 


breeding  periods.  Division,  growth  and  maturation  may 
often  be  found  side  by  side  in  a  single  reproductive  organ. 
But  these  external  phenomena  are  mere  curiosities  of  cell 
behavior,  until  we  inquire  what  is  going  on  inside  the  cells. 


INHERITANCE 


299 


.^P. 


0 


«  V  Ml, 


Fig.  178.  Diagram  of  the  sepa- 
rate maintenance  of  paternal 
and  maternal  chromosomes 
as  seen  in  certain  hybrids. 
5^,  sperm;  o,  egg;  a,  the  form 
of  the  chromosomes  of  the 
sperm;  b,  the  form  of  the 
chromosomes  of  the  egg;  w, 
fertilization  about  to  take 
place;  x,  the  nucleus  in  its 
succeeding  resting  stage;  y, 
the  reappearance  and  group- 
ing of  the  two  sorts  of  chrom- 
r)mes  at  a  subsequent  divi- 
sion; z,  division  of  the  cyto- 
plasm. The  condition  in  each 
nucleus  is  diagrammatically 
indicated  by  the  circles  below. 


Fertilization  and  maturation. — 

The  existence  of  sperm  cells  has 
been  known  ever  since  the  great 
pioneer  Dutch  naturalist  Leeuwen- 
hoek  and  his  pupils  with  home 
made  lenses  found  them  in  the 
seminal  fluid  of  animals,  but  they 
were  long  regarded  as'  'wild  animal- 
cules." In  1875,  Oscar  Hertwig 
established  the  fact  that  fertiliza- 
tion consists  in  the  union  of  one 
egg  and  one  sperm  only,  showing 
that  in  sexual  reproduction  each 
parent  contributes  one  cell  of  its 
own  body  to  the  formation  of  the 
young.  Then  it  became  evident 
that  the  sexes  play  an  equal,  al- 
though not  necessarily  an  identical 
role,  in  hereditary  transmission. 
This  conclusion  was  strongly  re- 
enforced  by  the  important  dis- 
covery of  Van  Beneden  (1883), 
that  germ  cells  contain  but  half 
the  number  of  chromosomes  that 
is  normal  to  the  body  cells  of  their 
own  species.  It  became  evident, 
therefore,  that  reduction  and  fer- 
tilization are  complemental  pro- 
cesses, the  one  leaving  each  sex 
cell  with  but  a  half  stock  of  chro- 
mosomes, ■'"he  other  restoring:  to 
the  fertilized  egg  cell  the  normal 
number.  At  the  same  time,  the 
sperm  introduces  new  elements 
into  the  lineage  of   the  egg  cell; 


300  GENERAL  BIOLOGY 

the  new  organism  must  differ  in  composition  from  the  old. 

Every  organism,  therefore,  that  is  developed  from  a  fer- 
tilized egg  sets  out  in  life  with  a  material  endowment  that  is 
derived  from  two  antecedent  cells.  In  its  nuclear  equip- 
ment there  are  two  more  or  less  unlike  sets  of  chromosomes. 
It  is  probable  that,  by  the  precise  mitotic  method,  the  sub- 
stance of  both  paternal  and  maternal  chromosomes  (fig.  178) 
is  equally  divided  and  distributed  at  every  cell  division. 
We  can  see  that  this  is  so,  when  paternal  and  maternal 
chromosomes  are  visibly  different  in  form,  as  is  notably  the 
case  in  certain  species  that  may  be  hybridized;  for  in  the 
hybrid  embryos  two  sorts  of  chromosomes  reappear,  con- 
stant in  number  and  form  and  grouped  by  themselves,  in 
successive  cell  divisions. 

Chromosomes. — -Protoplasm,  the  physical  basis  of  life,  is 
of  course,  the  material  basis  of  heredity.  Among  proto- 
plasmic structures,  those  of  the  nucleus  maintain  the  great- 
est permanence  and  uniformity  of  behavior.  The  chromo- 
somes especially  give  evidence  of  continuing  individuality  of 
organization.  What  the  chromosomes  are  we  do  not  know. 
That  they  are  chemical  substances  is  indicated  by  their 
micro-chemical  reactions;  it  is  by  means  of  their  reactions 
to  specific  stains  that  we  are  able  to  bring  them  clearly  into 
view.  Their  vital  organization  is  complex.  That  they 
play  an  important  role  in  cell  division  is  sufficiently  obvious ; 
mitosis  might  well  have  for  its  object  the  equitable  division 
of  them  among  the  descendent  cells.  That  their  role  in 
sexual  reproduction  is  likewise  important  is  indicated  by 
their  uniform  and  parallel  behavior  in  egg  and  sperm  while 
cytoplasmic  parts  are  undergoing  the  greatest  differentia- 
tion. 

Naturally,  the  greatest  speculative  interest  has  centered 
about  the  chromosomes.  They  have  been  assumed  to  be 
the  bearers  of  hereditary  characters,   and  the   agents  of 


INHERITANCE  301 

transmission.  Imagination  has  proceeded  beyond  the 
limits  of  vision,  and  has  pictured  them  composed  of  "bio- 
phores,"  "ids"  "determinants,"  and  other  hypothetical 
structures,  capable  of  handing  down  unit  characters  in 
inheritance.  The  existence  of  these,  or  of  any  other  such 
mechanism,  is  not  at  present  capable  of  either  proof  or  dis- 
proof; and  need  not  detain  us  here.  But  we  may  note  in 
passing  that  some  progress  has  been  made  in  relating  charac- 
ters of  the  adult  organism  to  characters  of  the  chromosomes 
of  the  germ  cells.  An  excellent  example  is  furnished  by  the 
so-called  "accessory"  or  sex-accompanying  chromosome  of 
certain  Hemiptera  and  other  arthropods.  In  the  squash 
bug,  for  instance,  in  the  body  cells  of  the  female  there  are  22 
chromosomes;  in  the  male,  but  21.  In  the  cells  of  this  sex 
one  chromosome  exists  unpaired,  all  the  others  are  joined  in 
pairs.  In  the  maturation  of  the  sperm  mother  cells,  the 
division  that  occurs  without  the  previous  splitting  of 
chromosomes,  leaves  an  odd  chromosome  in  half  the  cells. 
The  resultant  sperm  cells,  odd  and  even  in  their  chromosome 
complement,  unite  with  the  full-equipped  egg  cells,  as 
indicated  in  the  accompanying  diagram,  to  produce  new 
male  or  female  organisms,  according  to  the  chromosome 
distribution.  This  accessory  chromosome  (fig.  179),  w^hich 
the  female  zygote  only  receives,  is  sometimes,  as  in  the  plant 
bug  {LygcBus)  accompanied  by  a  small  mate,  {y,  of  the 
figure) ,  which  in  fertilization  only  the  male  offspring  receive. 
This  is  a  further  evidence  of  the  connection  between  the 
accessory  chromosome  and  the  sex  of  the  adult. 

Chromosome  reduction  occurs,  apparently,  in  all  the 
higher  organisms,  both  plants  and  animals,  but  the  attend- 
ant circumstances  appear  not  always  to  be  the  same.  It  is 
ever)rwhere  a  preliminary  to  fertilization.  In  the  higher 
plants  it  occurs  at  the  time  of  spore  formation;  and  the 
spores  and  all  the  cells  of  the  gametophyte  phase,  as  well  as 


30  2 


GENERAL   BIOLOGY 


eggs  and  sperms,  contain  half  the  number  of  chromosomes 
that  are  found  in  the  cells  of  the  sporophyte.  Thus,  reduc- 
tion and  fertilization  are  widely  separated  in  point  of  time. 
Two  divisions  of  the  spore  mother  cell  with  only  one  splitting 
of  the  chromosomes,  result  in  these  cells  issuing  with  the  half 


Maturing  divisions 
of  the  sperm  cells     Sperms  Eggs 


Actual 
number  of 
somatic 
chromo- 
Zygotes   somes 


W^  feo)  + 


^ygaeux 


A-  f%@  + 


Anasa 


C^2I 


Fig.  179.  Diagram  illustrating  the  behavior  of  the  "accessory," 
sex-accompanying  chromosome  in  fertilization  (after  Wilson). 
For  the  sake  of  clearness,  but  four  other  chromosomes  are 
shown,  and  these  four  diagrammatically ;  accessory  {x) ,  solid 
black. 

number  in  each,  just  as  in  the  egg  and  sperm  mother  cells 
of  the  higher  animals.  If  x  represent  the  number  of  chromo- 
somes in  the  sex  cells,  these  relations  may  be  expressed  by 
the  formula: 

The  higher  f  sperm  i^Wzy^ote  (2x)   The  new  individual  (2x)  f  sperm  (x) 

animals        I  egg        (x)  /  I  egg        (x^ 

The  higher  f  sperm  (x)  \  Zygote,  Sporophyte  (ax)  Spores  (x).Gameto-r  sperm  (xj 
plants  I  egg        (x)/     ^^       '     ^       i^    y      k     ,      f  phyte(x)legg       (x) 

Differentiation  of  the  cytoplasm  of  the  egg. — There  is  also 
definiteness  of  organization  in  the  cytoplasm  of  the  egg. 
Conklin  has  shown  that  in  the  egg  of  the  ascidian  Cynthia 
there  are  three  kinds  of  protoplasm  that  are  quite  different 


INHERITANCE 


3^3 


Fig.  180.  Eggs  of  the  ascidian 
Cynthia  showing  differentia- 
tion of  organ  forming  sub- 
stances in  the  cytoplasm, 
lateral  views  (after  Conklinj. 
a.  unsegmented,  but  a^ter 
fertilization;  b,  in  the  eight- 
cell  stage. 


in  their  appearance  and  also  in  their  destination  in  the  tis- 
sues, i)  There  is  a  clear  protoplasm  that  will  develop  into 
the  ectoderm;  2)  there  is  a  gray,  yolk-filled  protoplasm  that 
will  develop  into  endoderm,  and  3)  there  is  a  yellow  proto- 
plasm that  will  develop  into  mesoderm.  In  figure  180  these 
are  imperfectly  delimited,  the  yellow  protoplasm  being 
diagrammatically  indicated  by  the  heavier  stippling,  and 

the  gray  by  the 
intermediate  stip- 
pling; a  repre- 
sents the  egg  half 
an  hour  after  the 
entrance  of  the 
sperm  cell,  but  before  the  first  division; 
the  yellow  protoplasm  has  taken  up  its 
position  in  a  crescent  across  one  side  of  the 
egg,  half  of  it  being  shown  in  the  figure. 
The  first  cleavage  plane  (median  plane  of 
the  body  to  be  formed  later)  will  be  in  the 
plane  of  the  paper,  dividing  these  sub- 
stances symmetrically;  6  is  a  corres- 
ponding view  in  the  8-cell  stage,  with  the 
polar  bodies  still  persisting  at  the  upper 
pole,  and  the  yellow  protoplasm  occupying  a  part  only  of 
two  cells  of  the  lower  hemisphere,  while  most  of  the  gray 
protoplasm  has  withdrawn  into  the  other  two.  The  yellow 
protoplasm  will  all  develop  later  into  the  early  muscle  seg- 
ments lying  alongside  the  notocord.  Here  we  have  definite, 
predetermined  materials  for  the  making  of  the  embryo, 
which,  though  differing  in  kind  do  not  correspond  with  cell 
boundaries  and  which  are  therefore,  clearly  unrelated  as  yet 
to  chromosome  behavior. 

Synapsis. — There  is  another  process  that  is  believed  to 
intervene  in  the  case  of  many  of  the  higher  animals  and 


304  GENERAL  BIOLOGY 

plants  at  least.  At  the  beginning  of  the  growth  period  that 
precedes  the  two  maturation  divisions  there  occurs  a  fusion 
of  the  chromosomes  within  the  nucleus  in  pairs,  apparently 
with  like  paternal  and  maternal  elements  in  each  pair  (these 
elements  having,  since  the  preceding  fertilization,  main- 
tained themselves  apart,  although  in  one  nucleus).  This 
fusion  is  called  synapsis.  It  brings  into  more  intimate  asso- 
ciation the  equivalent  paternal  and  maternal  units,  appar- 
ently commingling  their  substance,  and  possibly  merging 
the  influences  they  have  borne  separately  since  the  preced- 
ing fertilization  brought  them  together. 

Parthenogenesis. — New  individuals  develop  from  eggs, 
and  not  from  sperms  alone,  but  either  eggs  or  sperms  alone 
seem  to  have  the  necessary  nuclear  equipment  for  the  com- 
plete development  of  new  individuals;  the  eggs  alone,  have 
the  cytoplasmic  equipment  necessary.  In  many  large  and 
widely  separated  groups  of  animals,  (aphids  and  other  in- 
sects, daphnids  and  other  crustaceans,  rotifers,  etc.),  there 
occurs  habitually  the  development  of  eggs  without  fertil- 
ization. This  is  called  parthenogenesis  (parthenos,  virgin  and 
genesis) .  In  the  honey  bee,  all  the  drones  are  believed  to  be 
developed  from  unfertilized  eggs.  This  phenomenon  is 
usually  an  accompaniment  of  peculiar  conditions  of  life,  and 
it  alternates  at  longer  or  shorter  intervals  with  true  sexual 
reproduction. 

In  the  vast  majority  of  organisms,  however,  the  addition 
of  the  sperm  to  the  egg  is  a  necessary  stimulus  that  must  be 
supplied  before  development  proceeds.  But  the  eggs  of  a 
number  of  animals  that  ordinarily  require  fertilization  can 
be  artificially  stimulated  to  develop  by  temporary  immer- 
sion in  proper  alkaline  solutions. 

The  sperm  nucleus  also  totipotent. — If  an  egg  be  deprived 
of  its  nucleus,  the  cytoplasm  dies ;  it  has  no  power  to  develop 
alone.     But  enucleated  eggs  have  been  fertilized  and  caused 


INHERITANCE  305 

to  develop  by  the  experimental  addition  of  sperm  cells  (fig. 
207);  the  sperm  cell  enters  as  it  would  to  fertilize  the  egg 
nucleus,  but  instead,  takes  the  place  of  that  nucleus,  and 
then  development  proceeds.  Evidently  the  necessary 
nuclear  equipment  for  development  is  present  in  the  sperm 
as  well  as  in  the  egg,  and  is  duplicated  in  the  zygote  in  cross 
fertilization. 

The  chief  facts  now  before  us,  regarding  the  material  basis 
for  inheritance  are  : 

1.  The  continuity  of  the  germ  plasm  through  the  genera- 
tions. 

2.  In  cell  division,  mitosis,  a  process  apparently  well 
fitted  for  carrying  development  forward  along  the  even 
tenor  of  its  way. 

3.  In  sexual  reproduction,  fertilization,  a  process  ap- 
parently well  fitted  for  introducing  new  elements  into  cell 
lineage. 

4.  Preliminary  to  fertilization,  synapsis  and  chromosome 
reduction. 

5.  The  development  of  eggs  without  fertilization  in  cases 
of  parthenogenesis. 

6.  The  duplication  of  the  chromosome  content  of  the 
nucleus  in  fertilization. 

Study  jy.     Observations  on  cell  division,  and  on  the  matur- 
ation of  sex  cells. 

Materials  needed:  Prepared  slides  showing  clearly  the 
chief  phenomena  of  cell  division,  either  in  growing  tissues  or 
in  developing  egg  cells.  Freshly  laid  and  living  eggs  of  pond 
snails  showing  polar  bodies. 

The  student,  duly  cautioned  as  to  the  damage  wrought  in 
tissues  in  section  making,  and  expedited  somewhat  in  his 
observations  by  the  guidance  of  the  teacher  (a  demonstra- 
tion with  projection  microscope  will  for  these  purposes  be 


3o6  GENERAL  BIOLOGY 

most  serviceable)  should  study  the  sections,  identifying 
successive  division  phases,  and  should  sketch  at  least  the 
spireme,  splitting  chromosomes  and  a  complete  spindle  with 
the  chromosome  complex  upon  it. 

Newly  laid  eggs  of  pond  snails  will  show^  the  formation  of 
the  polar  bodies  (in  external  aspect ;  not  chromosome  con- 
tent), and  as  these  persist  to  the  8-cell  stage  or  later  they 
may  be  found  and  sketched  in  outline  in  relative  proportion 
to  the  egg  to  which  they  are  attached. 

The  record  of  this  study  may  consist  of  notes  and  sketches 
of  the  principal  things  observed. 

Study  jS.     Observations  on  parthenogenesis .* 

Materials  needed:  Growing  plants  of  cabbage,  turnips 
or  lettuce  (or  any  other  green  house  plant  that  may  be  more 
convenient),  infested  with  viviparous  parthenogenetic 
female  aphids;  also,  small  individual  plants  growing 
in  thumb  pots,  and  covers  for  them  (see  appendix). 

The  student  should  isolate  a  newly  born,  (or,  at  least,  a 
very  young)  aphid,  transferring  it  (to  avoid  injury)  on  the 
point  of  small  camel's  hair  brush  to  an  uninfested  lettuce 
plant  in  thumb  pot,  and  covering  it  as  in  a  cage.  He  should 
keep  the  plant  growing  and  watch  the  reproduction  of  the 
aphid  from  time  to  time,  recording  progress  at  each  observa- 
tion. 

Continue  through  the  lifetime  of  a  single  individual  at 
least,  so  that  data  may  be  available  for  calculating  possible 
progeny  and  rate  of  increase  for  a  season.  Note  recurrence 
of  birth  of  young,  and  total  absence  of  males  during  the 
experiment.  Add  to  your  record  of  this  experiment  at  each 
time  of  observation;   trust  nothing  to  memory.     After  the 


*This  is  a  running  experiment,  covering  a  number  of  weeks  at 
least,  but  it  will  require  only  a  few  moments  observation  each  week 
after  it  is  started. 


INHERITANCE  307 

isolated  aphid  begins  to  bear,  remove  the  young  as  fast  as 
found  to  the  leaves  of  the  second  enclosed  plant,  leaving  the 
original  aphid  alone,  for  certain  determination  of  the  num- 
ber of  her  progeny.  Observe  in  the  other  cage  the  time  of 
beginning  of  reproduction  on  the  part  of  the  descendent 
aphids. 

The  record  of  this  study  may  consist  of  diagrams  illus- 
trating the  method  used,  and  a  statement  of  observations 
made. 

II.    THE   OBSERVABLE   RESULTS  OF  INHERITANCE. 

As  bearing  on  the  points  just  cited,  we  may  note  that 
many  facts  indicate  the  uniformity  of  development,  when 
cell  increase  proceeds  by  regular  mitotic  division,  and,  on 
the  other  hand,  that  marked  changes  result  from  cross  fer- 
tilization. This  is,  perhaps,  most  familiar  to  the  horticul- 
turist, who  maintains  his  choice  varieties  of  fruits  by  rigid 
adherence  to  asexual  methods  of  propagating  them,  (cut- 
tings, layers,  stolons,  buds,  etc.),  well  knowing  that  cross 
fertilization  would  introduce  new  characters  to  modify  (and 
from  his  point  of  view,  to  deteriorate)  his  commercially 
valuable  strains.  The  breeder  of  domesticated  animals  has 
not  this  advantage.  He  can  increase  his  flocks  only  by 
bisexual  reproduction.  Hence,  he  must  isolate  his  pure 
bred  individuals  in  order  to  maintain  the  purity  of  his  stock. 
This  is  the  key  to  the  efficiency  of  isolation,  as  well  in 
nature,  as  in  plant  or  animal  industry. 

Pure  breeds  and  hybrids. — In  nature,  the  individuals  of  a 
species  usually  present  great  uniformity  of  appearance. 
They  "breed  true."  But  in  some  wild  species  there  are 
diverse  forms  more  or  less  constantly  appearing.  Some- 
times group-differences  are  correlated  with  habitat,  as  in  the 
case  of  the  spermophiles  (ground  squirrels)  of  our  Pacific 
slope,  where  nearly  every  valley  has  its  own  peculiar  variety 


^o8  GENERAL   BIOLOGY 

Sometimes  they  are  found  side  by  side,  as  are  the  long  winged 
and  short  winged  crickets  of  the  Eastern  States,  or,  they  may 
be  related  to  season,  as  are  three  forms  of  the  Ajax  butterfly. 
Species  that  have  been  long  domesticated  always  show 
greater  diversity,  due  to  man's  influence  in  selecting  and 
isolating  the  most  divergent  types — especially  such  types  as 
natural  selection  would  ruthlessly  eliminate.  This  is  the 
only  way  of  obtaining  new  forms.  We  cannot  compel 
nature  to  produce  anything ;  we  can  only  wait  upon  her,  and 
preserve  our  choice  of  what  she  offers,  from  the  swamping 
effects  of  intercrossing  and  from  the  rigors  of  a  harsh  environ- 
ment. When  the  breeder  of  plants  or  animals  wishes  to 
obtain  a  new  strain,  he  breeds  together  forms  that  differ 
with  respect  to  the  characters  of  which  he  desires  to  secure  a 
modification.  This  is  hybridization.  If  all  the  offspring 
of  any  given  variety  that  is  bred  inter  se,  are  like  in  any  given 
character,  they  may  for  all  practical  purposes  be  considered 
in  respect  to  that  character  pure  bred. 

Types  of  inheritance.— What  the  result  will  be  when  any 
two  varieties  are  crossed,  what  characters  the  offspring  will 
bear,  can  only  be  determined  by  trial ;  it  will  always  be  the 
same  between  the  same  two  pure  varieties.  Observations 
on  matters  of  this  sort  fall  outside  the  possible  scope  of  the 
practical  studies  of  this  course;  we  will  content  ourselves, 
therefore,  by  noting  in  passing  a  few  of  the  more  general 
phenomena  of  hybridization. 

As  to  heritability  of  results,  the  offspring  may  be  sterile, 
and  therefore,  self-annihilating.  The  best  known  example 
is  the  mule,  a  cross  between  the  horse  and  the  ass.  There  is 
no  race  of  mules;  other  mules  are  to  be  obtained  only  by 
repeating  the  crossing  of  the  parent  species.  Or,  the  hy- 
brids may  be  relatively  stable,  and  breed  true,  as  single  new- 
formed  race  from  the  beginning.  The  garden  sunberry,  a 
cross  between  two  wild  inedible  species  of  Solanum,  is  said 


INHERITANCE 


309 


to  be  an  example,  and  there  are  many  others  among  culti- 
vated plants.  Or,  they  may  be  unstable,  as  in  the  great 
majority  of  cases,  some  of  which  will  be  illustrated  further 
on.  These  when  bred  inter  se  give  offspring  of  different 
sorts. 


GREGOR   MENDEL 

C1822-1884) 

Pioneer  student  of  hybridization;  discoverer  of  the  "law  of 

dominance." 

The  characters  that  the  hybrids  bear  may  be  only  the 
characters  of  their  parents,  or  they  may  be  new  characters 
of  their  own,  the  following  types  of  the  latter  being  com- 
monly recognized : 


2IO  GENERAL  BIOLOGY 

i)  Blended  inJieritance.  The  offspring  may  possess 
characters  intermediate  between  those  of  the  parents.  If 
one  parent  be  short  and  the  other  tall  the  offspring  may  all 
be  of  intermediate  height. 

2)  Intensified  inJieritance.  The  offspring  may  be  more 
extreme  than  either  parent.  If  one  parent  be  dark  and  the 
other  light,  the  offspring  may  be  darker  than  the  dark 
parent. 

3)  Heterogeneous  inheritance.  The  offspring  may  ex- 
hibit characters  differing  in  kind  from  those  of  either  parent. 
Certain  races  of  white  and  buff  pigeons  when  bred  together 
give  slate  colored  offspring.  Possibly,  more  knowledge  of 
the  characters  involved  in  such  cases  may  show  them  less 
lawless  than  has  been  thought. 

Alternative  inheritance.  When  parental  characters  are 
preserved  in  the  hybrids,  unfixed  and  unaltered,  we  have 
alternative  inheritance — the  type  that  has  hitherto  received 
most  attention,  and  which  in  its  behavior  seems  to  offer  the 
closest  parallel  to  the  behavior  of  the  chromosomes.  The 
offspring  of  the  first  generation  exhibit  the  characters  of 
one  parent  or  of  the  other ;  but  when  these  hybrids  are  bred 
together,  in  their  offspring  the  characters  of  both  parents 
reappear.  In  the  first  generation  hybrids  one  character 
appears  (is  dominant) ,  and  the  other  disappears  (is  latent 
or  recessive).  Both  characters  are  present,  but  both  cannot 
appear  at  the  same  time ;  a  flower  cannot  at  the  same  time 
be  fragrant  and  scentless.  Both  have  been  inherited,  how- 
ever, along  with  or  by  means  of  the  duplicate  apparatus  for 
conditioning  egg  development,  and  in  succeeding  genera- 
tions the  parental  characters  will  reappear.  This  type  of 
behavior  among  hybrids  was  first  studied  carefully  by 
Gregor  Mendel,  and  is  often  called  Mendelian  inheritance. 


INHERITANCE  311 

Mendel's  great  service  lay  in  a  long  series  of  carefuJ 
hybridizing  experiments,  from  which  the  principle  was 
deduced  that  whatever  the  appearance  of  the  hybrid,  it  pro- 
duces germ  cells  like  those  of  its  parents  in  approximately 
equal  numbers,  and  the  character  of  its  own  offspring  will  be 
determined  by  the  way  in  which  these  germ  cells  are  paired 
in  fertilization.  Suppose,  for  illustration,  that  D  and  R 
of  the  accompanying  diagram  (fig.  181)  represent  the  two 
parents,  which  differ  in  one  character  only,  that  of  color. 
D  is  black  and  R  is  w^hite.  Suppose  also  black  to  be  the 
dominant  and  white  the  recessive  color.  Then  the  offspring 
in  the  first  generation  (F  J  will  all  be  black.  But  if  they  be 
bred  together,  their  offspring  will  be  both  black  and  white 
in  the  proportion  of  three  black  to  one  white.     Then,  if  the 

whites  be  again  bred  together,  all 

©^-^  their  oft'spring  will  be  white.  The 
(  ^  )  white  character  which  disappeared 
in  the  first  hybrids,  was  obviously 
still  present,  and  has  been  sorted 
out  again.  This  relation  between 
characters   in   the    germ   cells   has 

©^!^    f^~^    been  aptly  compared  to  the  putting 
^g/^     \^__y     together  in  pairs  of  pieces  of  glass 

of  two  kinds,  one  transparent,  the 

^'L^\r^S^'''E:''^e    Other    opaque;    when    placed 

tfsfwf  f^^Tf^^  £    together  only  the  opaque  one  is  visi- 

b?Ms'?esp4tfvdr''°''  ''^'    ble,but  when  again  separated,  both 

are  again  apparent. 

If,  as  Mendel  supposed,  the  germ  cells  possessing  the  two 
characters  separately,  are  present  in  equal  numbers  in  the 
reproductive  organs  of  the  hybrids  and  are  combined  in  pairs 
according  to  the  law  of  chance,  there  are  but  four  possible 
combinations  of  them,  giving  three  classes,  as  indicated 
on  succeeding  page: 


© 


31 


GENERAL  BIOLOGY 

DandR,    germ  cells   of   one    hybrid  parent 
I  X  I  ^^  chance  combination  with 

DandR,    germ  cells  of  the  other  hybrid  parent 
give  in   the  second  (F^)  generation, 


DD  +  2DR  +  RR     in  the  proportion,  (3  black:  i  white)  n. 

Otherwise  stated,  if  any  two  of  these  hybrids  be  bred 
together  there  result  the  following  possible  combinations 
of  their  characters  in  their  offspring  (the  characters  D  and 
R  of  one  parent  being  underscored  in  order  to  distinguish 
sources) : 


n  and  D,  uniting,  give  D,  a  pure  dominant 
DandR,        "  "    DR 

R  and  D,        "  "    DR 


hybrids 


black 


R  and  R, 


R,  a  pure  recessive — white. 


Of  the  black  individuals  it  is  obvious  that  there  are  two 
classes  although  all  look  alike;  for  one  individual  out  of 
every  three  is,  like  the  white,  pure  bred  containing  sex  cells 
of  one  kind  only,  while  the  other  two  are  still  hybrid  in 
character.  The  further  results  of  intercrossing  of  like  with 
like  in  successive  generations  is  indicated  by  the  following 
table : 

Parents.  Offspring,  {mated  like  with  like.) 


Generation  I 

Gen.  II 

Gen. Ill 

Gen.  IV 

D] 

f  iD D 

D 

iD..    . 

D 

'3  < 

r3-, 

(.       \'^ 

>  .D(R)..  .  < 

[2D(R)< 

^2D(R). 

]^       (2D(R) 

iR 

1  iR 

R 

R  1 

1  iR 

.R 

.R 

INHERITANCE  313 

Mendel's  law  assumes  that  the  gametes  bearing  the 
characters  of  the  two  parents  are  produced  in  equal  num- 
bers, and  distributed  at  pairing  in  accordance  with  the  law 
of  chance;  and  this  assumption  is  not  contradicted  by  the 
known  facts.  And  since  it  offers  a  simple  mathematical 
basis  for  calculating  the  results  of  a  variety  of  crosses,  it  may 
readily  be  tested,  as,  for  example,  by  backcrossing  a  hybrid 
with  an  individual  of  either  parent  stock.  If  mated  with 
the  recessive  stock,  the  result  should  be  as  follows  (given,  of 
course,  as  for  any  test,  a  sufficient  number  of  offspring) : 

DandR,  germ  cells  of  the  hybrid  parent 
I  y^  I         in  chance  combination  with 
RandR,  germ  cells  of  the    recessive    parent, 
give  in  the  second  (F  J  generation. 


2D  (R)*  +  2RR     i.  e.,  50%  of  each  color. 

In  the  more  typical  cases  of  alternative  inheritance,  all 
the  foregoing  proportions  have  been  substantially  realized 
in  breeding  experiments. 

When  the  parents  differ  in  two  or  more  characters,  the 
hybrids  bearing  germ  cells  that  bear  all  these  characters 
severally,  will  effect  new  combinations  of  them,  and  forms 
differing  from  either  parent  will  appear  in  the  second  and 
later  generations.  If  we  let  X  and  Y  represent  the  dominant 
and  X  and  y  the  recessive  phase  of  two  characters  (as,  for 
example,  eye  color  and  hair  length)  there  will  appear  in  the 
second  generation,  besides  the  unstable  hybrid  forms,  the 
stable  forms  XXYY,  XXyy,  xxYY,  and  xxyy.  Which- 
ever two  of  these  represent  the  combination  of  characters 
found  in  the  parents,  the  other  two  are  new  combinations. 
The  law  of  Mendelian  inheritance,  substantially  as  estab- 


*The  parenthesis  is  thus  used  as  a  convention  for    indicating  the 
recessive  character. 


3M 


GEXERAL   BIOLOGY 


lished  by  its  founder,  is  represented  in  the  accompanying 
table  (after  Castle). 


Number  of 

Differences 

between 

Parents. 

Visibly  Differ- 
ent Classes, 
each  contain- 
ing one  Pure 
Individual. 

Total 

Classes, 

Pure  and 

Hybrid. 

Smallest  Number 

of  Offspring 

allowing  one 

Individual  to 

each  Class. 

n 

2" 

3" 

4« 

]  Tested  by  Men- 
y  del  for  peas  and 
j  found  correct. 

I 
2 

3 

2 

4 
8 

3 

9 

27 

4 
16 

64 

4 

5 
6 

i6 

32 
64 

81 

243 
729 

256 
1024 
4096 

>  Calculated. 

Castle  has  proved  by  breeding  experiments  that  in  guinea- 
pigs  length,  pigmentation  and  roughness  of  coat  are  hair 
characters  that  are  separately  heritable,  and  that  in  crossing 
they  follow  fairly  Mendel's  laAV.  And  he  summarizes  his 
observations  as  follows: 

"This  experiment  illustrates  two  important  principles  in 
heredity:  First,  if  as  regards  the  hair  alone  there  exists 
such  a  variety  of  characters  separately  inheritable,  how 
great  must  be  the  number  of  such  characters  in  the  body  as 
a  whole,  and  how  remote  the  probability  that  any  animal 
will  in  all  characters  resemble  any  individual  ancestor,  pro- 
vided that  in  a  considerable  number  of  heritable  characters 
a  choice  is  offered  between  alternative  conditions.  Secondly, 
the  experiment  shows  how  a  variety  of  new  organic  forms 
may  quickly  be  produced  by  cross-breeding,  leading  to  the 
combination  in  one  race  of  characters  previously  found 
separately  in  different  races.  Thus,  in  guinea-pigs,  one  can 
obtain  within  two  generations  any  desired  combination  of 
the  three  pairs  of  alternative  coat-characters,  if  one  pro- 
duces a  sufficiently  large  number  of  individuals. 


INHERITANCE  315 

"From  what  has  thus  far  been  said  it  would  appear  that  in 
alternative  inheritance  characters  behave  as  units,  and, 
more  than  that,  as  wholly  indepe^tdent  units,  so  that  to  fore- 
cast the  outcome  of  matings  is  merely  a  matter  of  mathe- 
matics. While  this  is  in  a  measure  true,  it  is,  fortunately  or 
unfortunately,  not  the  whole  truth.  In  alternative  inheri- 
tance characters  do  behave  as  units  independent  of  one 
another,  but  the  union  of  dominant  character  with  recessive 
in  a  cross-bred  animal  is  not  so  simple  a  process  as  putting 
together  two  pieces  of  glass,  nor  is  their  segregation  at  the 
formation  of  gametes  so  complete  in  many  cases  as  the 
separation  of  the  two  glass  plates.  The  union  of  maternal 
and  paternal  substance  in  the  germ-cells  of  the  cross-bred 
animal  is  evidently  a  fairly  intimate  one,  and  the  segregation 
which  they  undergo  when  the  sexual  elements  are  formed  is 
more  like  cutting  apart  two  kinds  of  differently  colored  wax 
fused  in  adjacent  layers  of  a  common  lump.  Work  carefully 
as  we  will,  traces  of  one  layer  are  almost  certain  to  be  in- 
cluded in  the  other,  so  that  while  the  two  strata  retain  their 
identity,  each  is  slightly  modified  by  their  previous  union  in 
a  common  lump. 

"Thus,  when  we  cross  short-haired  with  long-haired  guinea- 
pigs,  we  get  among  the  second-generation  offspring  a  certain 
number  of  long-haired  animals  with  hair  less  long  than  that 
of  the  long-haired  grand-parent,  or  with  long  hair  on  part 
of  the  body  only. 

"Cross-breeding,  accordingly,  is  a  two-edged  sword  which 
must  be  handled  carefully.  It  can  be  used  by  the  breeder  to 
combine  in  one  race  characters  found  separately  in  different 
races,  but  care  must  be  exercised  if  it  is  desired  to  keep 
those  characters  unmodified.  If  modification  of  characters 
is  desired  at  the  same  time  as  new  com.binations,  then  cross- 
breeding becomes  doubly  advantageous,  for  it  is  a  means  of 
inducing  variability  in  characters,  as,  for  example,  in  the 


31 6  GENERAL  BIOLOGY 

intensity  of  pigmentation  and  in  the  length  of  hair,  quite 
apart  from  the  formation  of  new  groupings  of  characters. 
Sometimes  it  causes  a  complex  character  to  break  up  into 
simpler  units,  as  the  agouti  coat  of  the  wild  guinea-pig  into 
segregated  black  and  yellow,  or  total  pigmentation  into  a 
definite  series  of  pigmented  spots.  In  other  cases  it  operates 
by  bringing  into  activity  characters  which  have  previously 
been  latent  in  one  or  other  of  the  parental  forms. 

"Now,  what  bearing,  we  may  ask,  have  these  theoretical 
matters  on  the  practical  work  of  the  breeder?  They  show 
i)  that  a  race  of  animals  is  for  practical  purposes  a  group  of 
characters  separately  heritable,  and  2)  that  the  breeder 
who  desires  in  any  way  to  modify  a  character  found  in  this 
group,  or  to  add  a  new  character  to  the  group,  should  first 
consider  carefully  how  the  character  in  question  is  inherited. 

"If  the  character  is  alternative  in  heredity  to  some  other 
character,  cross-breeding  between  the  two,  followed  by 
selection  for  pure  individuals,  will  within  two  generations 
give  the  desired  combination  of  characters  in  individuals 
which  will  breed  true.  This  process  of  selection  is  simplest 
when  the  characters  to  be  combined  are  recessive  in  nature, 
but  individual  breeding-tests  become  necessary  when  domi- 
nant characters  are  included  in  the  combination  desired. 

"If  a  character  gives  blending  inheritance,  it  must  be 
treated  in  a  different  way.  Suppose,  for  example,  that  we 
desire  to  combine  lop-ears  in  rabbits  with  albinism,  but  that 
our  lop-eared  stock  consists  wholly  of  pigmented  animals. 
How  shall  we  proceed?  First,  mate  a  pigmented-lop  with 
a  short-eared  albino.  The  offspring  will  be  pigmented  half- 
lops.  If  two  of  these  be  bred  together  their  young  will  all 
be  half-lops,  and  about  one  in  four  of  them  will  be  albinos. 
Now  these  albino  half-lops  may  be  mated  with  pure  pig- 
mented lops.  The  young  will  again  all  be  pigmented,  but 
will  this  time  be  three-quarter  lops,  and  by  breeding  these 


INHERITANCE  •  317 

together  albino  three-quarter  lops  may  be  obtained  in  the 
next  generation.  By  continuing  this  process  of  back-cross- 
ing with  the  lop-eared  stock,  and  selecting  the  albino  off- 
spring obtained,  the  lop-eared  character  may  be  steadily 
improved  in  the  albinos  until  it  is  practically  as  good  as  in 
the  original  lop-eared  stock.  The  rate  of  improvement  pos- 
sible can  be  readily  calculated.     The  albino  young  will  be: 

After     2  generations,  one  half  lops, 

After    4  generations,  three  fourths  lops. 

After    6  generations,  seven  eighths  lops. 

After    8  generations,  fifteen  sixteenths  lops, 

After  10  generations,  thirty-one  thirty-seconds  lops,  etc. 

This  will  be  the  result  on  the  hypothesis  that  no  secondary 
variation  occurs  in  the  lop-eared  character.  If,  however, 
variation  is  induced  by  the  cross-breeding,  then  it  is  possible 
that  the  desired  end  may  be  reached  sooner,  or  that  an  even 
better  lop  may  be  obtained  in  the  albino  cross-breds,  than 
that  of  the  original  pigmented  stock. 

"Latent  characters  are  an  important  element  in  practical 
breeding.  Sometimes  they  greatly  aid  the  breeder's  work; 
sometimes  they  impede  it.  If  a  stock  contains  undesirable 
latent  characters  which  are  brought  into  activity  by  cross- 
breeding, these  latent  characters  will  have  to  be  eliminated, 
or  a  new  stock  tried." 

Obviously,  without  variation  no  new  characters  are 
obtained  by  such  intercrossing,  but  merely  new  combina- 
tions of  characters  that  previously  existed  apart.  But, 
when  new  characters  appear  among  the  variants  of  a  species, 
and  especially  when  a  number  of  new  characters  appear 
simultaneously  as  in  typical  cases  of  mutation,  then  inter- 
crossing may  be  the  means  of  bringing  these  characters 
together  in  all  sorts  of  combinations,  some  of  which  may  be 
of  value  to  man,  and  some  of  which  may  be  fit,  and  may, 
therefore,  furnish  a  basis  for  further  natural  evolution. 


3i8  GENERAL  BIOLOGY 

III.       NATURE     AND     NURTURE. 

The  germ  cells  constitute  the  bond  between  the  genera- 
tions. To  the  egg  and  the  sperm  we  must  look  for  sources 
of  hereditary  characters. 

The  human  species  inherits  as  do  the  other  organisms. 
Characters  of  various  sorts  "run  in  families;"  form  charac- 
ters, such  as  shape  of  nose,  of  chin,  of  fingers;  physiological 
characters,  such  as  left-handedness,  baldness  (in  males), 
slenderness  or  corpulence,  etc. ;  psychological  characters, 
such  as  emotional  or  judicial  type  of  mind,  phlegmatic  or 
effervescent  temperament,  etc.  But  most  of  these  are 
examples  of  complexes  of  characters,  that  must  be  analyzed 
to  their  component  units  before  their  manner  of  inheritance 
can  be  studied.  To  speak  of  infectious  diseases  as  being 
hereditary  is  wholly  inaccurate,  for  disease  germs  are  not 
part  of  the  body,  but  foreign  organisms ;  they  can  be  passed  on 
from  one  generation  to  another  only  by  infection,  and  not 
by  inheritance.  There  may,  however,  exist  innate  physio- 
logical weakness  that  favors  the  infection  in  successive  gener- 
ations, and  infection  may  occur  before  birth  as  well  as  after. 

However  much  the  young  may  receive  of  fostering 
parental  aid  in  yolk,  in  shelter  within  or  without  the  body, 
in  nourishment  by  means  of  embryonic  membranes,  etc.,  it 
has  already  received  when  egg  and  sperm  have  united,  its 
full  hereditary  endowment;   all  else  is  nurture. 

Inheritance  of  acquired  characters.  In  the  lifetime  of  the 
individual,  the  body  may  acquire  various  characters.  The 
skin  may  get  a  coat  of  tan  in  a  few  days  exposure  to  the  sun. 
The  hands  become  calloused  with  toil.  The  muscles 
strengthen  with  use.  Dexterity  results  from  practice,  and 
by  long  effort  we  may  acquire  an  education.  But  are  any 
of  these  things  which  the  individual  may  acquire  during  his 
lifetime  heritable,  or  does  the  offspring  start  at  the  common 
level  of  its   kind,   nothing   advantaged   by   whatever   his 


INHERITANCE  319 

individual  parents  may  have  gained  ?  This  is  an  exceed- 
ingly important  question,  the  answer  to  which  must  have 
something  to  do  with  determining  our  educational  policy. 

In  the  long  run  all  characters  are  acquired  characters,  if 
evolution  be  conceded.  The  question  is,  Can  the  peculiar 
conditions  which  cause  new  characters  to  develop  in  the 
body  so  affect  its  germ  cells  that  these  will  develop  the  same 
characters  in  the  next  generation,  even  in  absence  of  the  con- 
ditions that  first  called  them  forth  ?  When  we  remember 
the  early  isolation  of  the  germ  cells,  their  lack  of  participa- 
tion in  the  work  of  the  body,  and  their  remoteness  from  con- 
tact with  environment  this  seems  unlikely.  How,  for 
example,  could  the  abuse  of  the  eyes,  causing  partial  blind- 
ness in  the  adult,  so  affect  the  germ  cells  that  have  no  eyes, 
as  to  cause  them  to  develop  in  the  next  generation,  w4th 
proper  use,  the  same  weakness?  That  new  characters  are 
acquired  by  the  individual  body  needs  no  proof;  that  they 
are  at  the  same  time  acquired  by  its  germ  cells  is  not  proved, 
although  it  has  been  widely  believed.  Mutilations  of  the 
body  we  know  are  not  inherited.  The  loss  of  an  eye  in  one 
generation  does  not  prevent  its  perfect  development  in  the 
next.*  The  tails  of  sheep  have  been  docked  for  centuries, 
and  yet  lambs  continue  to  develop  tails  in  apparently 
undiminished  luxuriance. 

On  the  other  hand,  there  are  facts  showing  that  the  germ 
cells  (or,  at  least,  the  sex  organs,  collectively)  do  affect 
the  characters  of  the  body  of  which  they  are  an  isolated 
part.  The  effects  of  castration  (removal  of  the  spermaries) 
of  young  animals  are  often  very  marked.  The  differences 
between  a  bull  and  a  steer,  for  example,  are  very  apparent 
in  the  horns  and  neck  muscles,  in  voice  and  attitudes,  in 
disposition,  in  ability  to  put  on  fat  quickly,  and  in  other 


*"Wooden  legs  do  not  run  in  families,  but  wooden   heads  do." 

— Con  KLIN. 


320  GENERAL   BIOLOGY 

characters  that  are  equally  remote  from  the  missing  sex 
organs  of  the  latter.  Doubtless  the  condition  of  the  body 
does  affect  the  germ  cells  also  (whether  well-  or  ill-nour- 
ished; healthy  or  not,  but  in  what  manner  and  to  what 
extent  is  not  readily  determinable  at  the  present  day. 

The  physical  basis  of  racial  solidarity. — This  we  know; 
that  with  all  the  changes  of  its  outward  conditions,  human 
nature  changes  little.  .  Civilization  advances,  but  civiliza- 
tion concerns  itself  with  methods  of  nurture  alone ;  and  its 
gains,  every  individual  must  re-appropriate  for  himself. 
Nurture  creates  many  artificial  distinctions  among  men,  but 
their  nature  is  little  altered.  Good  health  and  good  spirits 
and  normal  desires  for  life,  liberty  and  the  pursuit  of  happi- 
ness are  not  the  possession  of  any  class  or  condition  of  men. 
Good  brains  are  probably  as  equitably  distributed  as  are 
good  muscles,  although  the  opportunity  for  their  develop- 
ment may  not  be.  Dynasties  may  rise  and  fall,  systems 
come  and  go,  but  the  racial  currents  run  on  serenely.  Art 
and  science  are  not  transmitted  in  the  germ;  the  only  part 
of  our  education  that  is  inherited  is  the  organic  part  of  it 
that  is  common  to  the  race.  Fortunately  or  unfortunately, 
the  springs  of  racial  progress  lie  very  deep ;  and  if  they  are 
not  readily  reached  by  humanitarian  effort,  they  are  at  least 
remote  from  unskillful  meddling.  It  is  the  common  stock 
of  germ  plasm  of  our  race  that  breeds  our  common 
interests  and  common  needs,  and  makes  it  possible  for  us  to 
have  common  schools  and  common  law.  This  is  the  great 
guarantee  of  democracy. 

Racial  differentiation. — Nevertheless,  our  common  stock 
of  germ  plasm  is  not  quite  homogeneous.  It  has  had  a  long 
history.  It  has  developed  divergent  tendencies.  It  has 
lived  under  different  environments.  The  spirit  of  one  people 
is  not  that  of  another.     That  the  slow  methods  of  nature 


INHERITANCE  321 

have  wrought  changes  in  the  constitution  of  her  segregated 
strains  appears  in  this;  their  civiHzations  differ,  and  though 
civilization  be  nurture,  the  capacity  for  it,  the  impulse 
toward  it  and  the  genius  to  modify  it  must  be  inherent. 
And,  if  this  is  true  of  tribes,  it  is  true  within  each  tribe,  on  a 
lesser  scale.  "Blood  does  tell."  To  some  extent  at  least 
genius  does  run  in  families,*  as  also  do  criminal  tendencies, 
the  capacity  for  the  development  of  either  being  organic. 
Hitherto  human  society  has  taken  little  account  of  these 
springs  of  future  character. 

The  meaning  of  nurture. — Most  organisms  give  little  nur- 
ture to  their  young.  They  merely  breed.  Their  innumer- 
able progeny  are  scattered  broadcast  in  a  pitiless  environ- 
ment, and  here  and  there,  by  chance,  one  survives.  De- 
struction is  the  rule;  survival  the  rare  exception.  We  have 
already  seen  in  our  study  of  the  plant  and  animal  series  how 
the  dominant  organisms  have  made  their  advantages  secure 
by  better  care  for  their  offspring  during  development;  by 
adding  food  to  the  egg  or  supplying  it  to  the  embryo,  and 
then  by  adding  housing  and  parental  care.  Ever,  there  is 
a  lessening  of  the  number  of  young  produced  coupled  with 
increase  in  the  care  for  them.  The  powers  of  the  body  are 
devoted  less  and  less  to  starting  new  individuals  in  life  and 
more  and  more  to  the  better  equipment  for  life  of  those  that 
are  produced.  The  lioness  of  the  fable  might  well  boast  that 
though  her  offspring  were  but  one  at  a  birth,  that  one  was  a 
lion ;  and  then  might  well  care  for  it  as  though  there  were  no 
lions  to  spare. 


*I  have  often  heard  false  pride  of  ancestry  condemned,  but  I  have 
not  seen  the  true  pride  of  ancestry  explained  and  commended. 
Surely  the  man  who  is  conscious  that  he  comes  of  stock  sound  in 
body,  able  in  mind,  tested  in  achievement,  and  who  knows  that, 
mating  with  like  stock  and  maintaining  himself  in  health,  he  may 
hand  down  that  heritage  to  his  children,  surely  such  a  man  may 
have  a  legitimate  pride  in  ancestry." — K.  Pearson 


322 


GENERAL  BIOLOGY 


The  eggs  and  sperms  of  some  of  the  lower  organisms  may 
be  mixed  in  a  glass  of  sea  water  and  watched  at  one  sitting 


Fig.  182.  Nest  and  eggs  of  the  musk  turtle  {Eremochelys  odorams). 
This  nest  was  made  in  an  old  muskrat  house.  Tiie  full  complement  of 
eggs  is  shown  below.     Photos  by  Hankinson  and  McDonald, 

through  fertilization  and  the  early  stages  of  development, 
until  they  are  ready  to  enter  actively  into  the  struggle  for 


INHERITANCE 


323 


life.  A  few  weeks  of  lying  in  the  sunwarmed  marsh  suffice 
for  the  hatching  of  the  eggs  of  the  musk  turtle  (fig.  182), 
which  receive  no  parental  care.  Three  weeks  of  persistent 
incubation  are  necessary  to  hatch  the  eggs  of  the  common 
fowl,  and  a  still  longer  period  of  maternal  care  after  hatch- 
ing is  needed  to  get  the  chicks  well  started  in  their  careers. 


Fig.  183.     Sandpiper  (precocious)  a  few  days  old,  swimming. 
Photo  by  G.  C.  Embody. 


The  young  of  altricial  birds  (fig.  184)  are  fewer,  hatch  in  a 
more  helpless  condition,  require  to  have  their  food  brought 
to  them  and  put  in  their  mouths,  and  receive  the  care  of  both 
parents  for  a  long  time.  Months  of  pre-natal  nur- 
ture are  required  for  the  development  of  the  young  of  all  the 
larger  mammals,  and  after  birth,  other  months  of  nursing,  of 


324 


GENERAL  BIOLOGY 


shelterino^,  of  care  and  assistance.     And  to  all  this  man  adds 
education,  which  is  only  an  extension  of  the  original  mother 


Fig.  184.      Young  marsh  hawks  (altricial)  some   days  old,  yet  hardly 
able  to  stand.      Photo  by  E.  McDonald. 

function.*  In  the  eye  of  the  law  it  takes  twenty-one  years 
to  make  a  man.  Thus,  human  society  has  learned  the  first 
lesson  of  racial  progress. 


*"And.  it  was  told  him,  Thy  mother  and  thy  brethren  stand  with- 
out, desiring  to  see  thee.  But  he  answered  and  said  unto  them, 
My  mother  and  my  brethren  are  these  which  hear  the  word  of  God, 
and  do  it."     Luke  8:20.21 


INHERITANCE  325 

Study  JQ.     Observations  on   the  relation  between  fecundity 

and  nurture. 

Materials  for  this  study  are  so  diverse  and  ever  present,' 
that  instead  of  a  definite  outHne,  the  following  suggestions 
of  typical  illustrations  are  offered: 

1.  In  order  that  the  enormous  numbers  of  young  pro- 
duced by  some  species  may  be  realized,  study  some  such 
thing  as  the  number  of  spores  produced  by  a  flowering  fern, 
or  seeds  by  a  cottonwood  tree.  Count  for  example  in  the 
fern  the  number  of  good  spores  in  an  average  sporangium, 
the  number  of  sporangia  on  a  sorus,  the  number  of  sori  on  a 
fruiting  frond,  the  number  of  f^-uiting  fronds  on  an  average 
plant,  and  multiply  together  for  totals,  multiplying  in  the 
end  by  the  number  of  years  of  fruiting  for  the  normal  life  of 
the  plant;  the  numbers  will  be  sufficiently  significant  even 
though  the  last  point  be  indeterminable.  If  done  by  a 
class,  the  averaging  of  the  collective  counts  will  give  better 
approximation  to  the  truth. 

2 .  For  observation  of  the  reduction  in  numbers  that  goes 
with  a  little  parental  care,  compare  number  of  young  pro- 
duced by  some  nesting  fish,  such  as  sunfish,  bass  or  bull- 
head, with  those  produced  by  a  pike  or  a  carp ;  for  this,  ripe 
ovaries  may  be  taken  and  their  content  counted  in  part  and 
estimated. 

3.  The  concomitants  of  more  extended  care  and  careful 
nurture  may  be  studied  by  comparing  the  number  of  young 
and  the  care  they  receive  in  the  precocious  and  altricial 
birds,  abundant  data  for  which  will  be  found  accumulated 
and  ready  to  hand  in  many  good  bird  books. 

The  record  of  this  study  may  consist  of  a  tabular  state- 
ment of  the  data  obtained. 

The  disturbance  of  the  natural  balance  by  conditions  o^ 
civilized    life. — The    rate    of   reproduction   established    by 


32  6  GENERAL  BIOLOGY 

nature  for  the  human  species  is  far  too  high  for  civilized 
conditions.  It  was  adequate  to  replace  the  losses  by  war, 
pestilence  and  famine  in  primitive  society.  But  now  that 
these  agencies  of  death  are  in  a  measure  controlled,  the 
natural  balance  is  disturbed.  Without  these  checks  the 
human  population  of  the  earth  is  rapidly  increasing. 

Many  wild  species  are  being  exterminated,  and  most  of 
them  are  being  reduced  in  numbers.  For  man  must  carry 
with  him  the  few  domesticated  species  on  which  his  livelihood 
depends,  and  wherever  he  spreads,  the  native  population  of 
the  earth  must  be  annihilated  to  make  room  for  his  fields  and 
stock  pens.  The  pressure  for  room  has  often  been  felt  in 
"congested  districts"  throughout  human  history.  With 
the  present  excess  of  birth  rate  over  death  rate,  the  whole 
habitable  earth  will  be  one  congested  district  soon.  Every 
triumph  of  science  over  plague  or  famine  or  other  casualty 
increases  the  pressure,  so  long  as  the  excessive  rate  of  in- 
crease continues. 

The  ideal  condition  of  society  is  that  toward  which  nature 
points  the  way  in  the  series  of  phenomena  we  have  just  been 
studying:  the  adjustment  permitting  the  normal  well-condi- 
tioned development  of  every  individual. 

There  are  biological  aspects  of  our  civilization  that 
are  not  reassuring: 

i)The  possibilities  of  the  germ  are  realized  only  in  the  in- 
dividual. Whatever  the  nature  of  it,  only  nurture  can  bring 
it  to  perfection  ;  and  nurture  is  still  largely  w^asted  among 
us  in  broken  lives. 

2)  The  weaklings  of  our  race  under  existing  conditions, 
not  only  survive,  but  they  usually  survive  to  perpetuate 
their  weaknesses  in  descendants. 

3)  There  are  processes  of  civilization  that  select  the  best 
for  elimination;  wars,  which  kill  off  the  strong  and  the 
brave  on  the  battlefield  and  leave  the  weak  at  home  to 
breed.     And  economic  conditions  that  take  the  brightest  of 


INHERITANCE  327 

the  children  of  the  poor  from  their  studies  and  their  play, 
and  set  them  prematurely  at  grinding  toil,  thus  hindering 
their  normal  development. 

4)  The  excess  of  offspring  is  mainly  coming  from  the 
lower  ranks  of  human  society.  Those  classes  that  are  most 
advanced  in  arts  and  education  are  hardly  reproducing 
themselves,  while  the  earth  is  being  over-populated  by  the 
descendants  of  the  less  progressive.  That  the  educated 
classes  are  not  taking  a  larger  share  in  the  building  of  the 
future  race  is  not  in  itself  a  necessary  evil,  for  education  is 
not  always  an  accompaniment  of  either  physical  or  moral 
fitness.  Indolence  and  self  gratification  and  the  cultivation 
of  low  desires  breed  degeneracy  in  rich  and  poor  alike. 
That  the  population  of  the  earth  in  the  immediate  fujture 
will  be  composed  mainly  of  the  sons  and  daughters  of  poor 
and  ignorant  parents  is  not  so  serious  a  matter  as  it  might  at 
first  appear;  for,  with  normal  aspirations,  property  and  edu- 
cation may  be  acquired,  and  the  lack  of  these  things  may 
be  due  to  accidents  of  birth  and  station.  But  the  danger  of 
qualitative  degeneration  lies  in  the  rapid  and  as  yet  almost 
unrestricted  breeding  of  the  physically  mentally  and  morally 
degenerate. 

The  increase  in  population,  which,  if  continued  at 
the  present  rate  would  certainly  bring  disaster,  is  mainly 
due,  strangely  enough,  to  the  progress  of  knowledge 
and  to  the  extension  of  humanitarian  effort.  These  have 
reduced  the  death  rate  for  all  classes  of  society,  while 
diminishing  the  birth  rate  for  only  the  better  educated 
classes.     It  is  thus  the  natural  balance  has  been  disturbed. 

In  the  cities  the  pressure  for  room  is  first  manifest;  and 
it  is  here  that  the  annihilation  of  the  green  earth  and  all  the 
host  of  living  things  belonging  with  it  is  completest.  Even 
here  in  times  of  peace  and  plenty  all  men  may  live  in  com- 
fort; but  when  the  pinch  of  famine  or  disaster  comes,  then 


328  GENERAL    BIOLOGY 

men  crowd,  as  do  the  beasts,  for  food  and  standing  room. 
And  whenever  and  wherever  they  crowd,  in  good  times  or 
bad,  they  make  such  use  of  the  earth's  resources  as  means 
irreparable  loss,  and  insures  that  the  crowding  of  the  future 
will  be  of  intensified  severity. 

The  greatest  problems  of  man's  future  upon  the  earth  are 
connected  with  better  breeding  and  better  nurture. 
Security  for  the  future  undoubtedly  lies  in  having  more 
knowledge,  and  in  making  such  use  of  it  as  will  yield  better 
results  in  racial  improvement  and  in  individual  develop- 
ment. 


CHAPTER  V. 
THE  LIFE  CYCLE. 

Among  the  simplest  organisms,  in  which  each  cell  may 
go  on  growing  and  dividing  indefinitely,  the  familiar 
phenomena  of  youth,  maturity,  and  old  age,  are  not 
apparent.  Every  cell  is  a  germ  cell,  and,  therefore,  ever 
young.  But  with  sexual  reproduction  comes  in  the  dual 
organism,  composed  of  body  plasm  and  germ  plasm,  only 
the  latter  continuing,  the  former  mortal. 

The  normal  life  cycle. — It  is  the  common  lot,  among  all 
organisms  except  the  lowest,  to  be  developed  from  an 
egg,  to  be  supplied  in  infancy  with  food,  to  pass  through 
hereditary  changes  of  form,  to  grow  and  reach  maturity 
to  exercise  for  a  longer  or  shorter  period  the  matured  powers 
of  the  body,  to  produce  offspring,  and  then  to  grow  old  and 
die.  Youth,  maturity,  and  age  follow  each  other  in  an 
orderly  progression  that  is  readily  definable  in  terms  of 
metabolism,  thus: 

1.  In  youth  the  building  up  processes  are  in  the  ascenden- 
cy. Assimilation  is  greater  than  dissimilation  (juvenescence). 

2 .  In  maturity  the  waste  and  repair  of  the  body  are  on 
a  parity.     Assimilation  is  equal  to  dissimilation. 

3.  In  age  the  building  up  processes  are  in  a  state  of 
relative  decline.  Assimilation  is  less  than  dissimilation 
(senescence) . 

Although  we  may  thus  state  in  metabolic  terms  the  his- 
tory of  the  body,  the  explanation  therefor  must  be  stated  in 
terms  of  reproduction.  It  is  necessary  for  the  organism  to 
establish  itself,  before  it  can  do  much  to  provide  for  pos- 
terity; hence,  the  nutritive  apparatus  of  the  body  is 
developed  first,  and  growth  precedes  reproduction.     The 


330  GENERAL  BIOLOGY 

period  of  adult  life  may  be  long,  as  in  elephants,  or  short,  as 
in  mayflies;  it  may  be  reached  by  a  gradual  and  regular 
development,  or  by  a  series  of  abrupt  form  changes;  but 
when  it  arrives  with  full  maturity  of  powers,  the  reproduc- 
tive process  takes  the  ascendency.  Primarily  it  is  the 
period  of  making  provision  for  descendants.  Whether 
such  provision  consist  merely  in  mating  and  depositing 
eggs,  or  whether  in  addition  to  this,  the  substance  of  the 
body  be  transformed  into  food  for  the  young,  or  whether, 
still  further,  the  physical  powers  of  the  body  be  devoted 
to  the  care  of  the  young,  or  whether,  finally,  as  in  human 
society,  with  long  years  for  individual  activity,  the  labors 
of  life  be  devoted  to  securing  for  posterity  the  betterment 
of  those  conditions  that  hinder  its  best  development,  it  is 
all  the  same ;  the  primary  concern  of  adult  life  is  provision 
for  the  future  of  the  race. 

The  regularly  progressive  life  cycle  is  sufficiently  familiar 
and  needs  no  further  illustration.  But  this  undergoes 
some  remarkable  changes  under  natural  conditions,  and 
other  alterations  of  it  may  be  caused  artificially.  Some 
of  the  more  typical  of  these  phenomena  will  now  be  con- 
sidered, under  the  following  headings:  i)  Alternation  of 
generations,  2)  Special  methods  of  asexual  reproduction, 
3)  Change  of  form  with  alternation  of  hosts,  4)  Meta- 
morphosis, 5)  Artificial  division  and  combination  of  or- 
ganisms. 

I.        ALTERNATION    OF    GENERATIONS. 

This  phenomenon  consists,  as  we  have  already  seen,  in 
the  establishment  of  two  segregated  phases  within  the  life 
cycle,  one  sexually,  and  the  other  asexually  reproducing. 
We  have  already  traced  the  development  of  it  in  gameto- 
phyte  and  sporophyte  of  the  higher  green  plants.  An 
equally  good  example  of  it  is  found  among  animals  in  the 
group    of   marine   hydroids.     Medusa    and   hydranth    are 


THE  LIFE  CYCLE 


331 


there  the  sexual  and  asexual 
phases  of  the  life  cycle  respec- 
t  i  V  e  1  y  .  The  free-swimming 
medusa  (jelly  fish,  fig.  185c) 
produces  the  eggs  and  sperms 
and  liberates  them  in  the  sea. 
These  after  fertilization  develop 
into  sessile  hydranths  (more  or 
less  similar  to  the  common  hy- 
dra) ,  which  in  turn  develop  me- 
dusae  by 

various  yj,  )|// // 

modes  of 
asexual 
budding. 


II.       SPECIAL     METHODS    OF    ASEXUAL 
REPRODUCTION. 

Sexual  reproduction  results  in  the 
main  in  a  qualitative  increase  in  a 
species.  Without  segregation  it 
tends  toward  reducing  all  the  forms 
to  a  common  level,  but  with  segrega- 
tion, whether  external  or  internal,  it 
is  a  potent  means  of  effecting 
species  change.  Asexual  reproduc- 
tion is  quantitative  vathev  than  quali- 
tative increase.     One   individual    is 

Fig.  185.  The  Colonial  hydroid  {Bougainvillea^ 
^,  the  form  of  a  small  colony,  b,  a  bit  from  the 
tip  of  one  of  the  branches;  w,  tentacles  of  a 
single  hydranth;  x,  y,  z,  stages  in  the  develop- 
ment of  the  buds  (medusae),  c,  The  fully 
formed  and  free  swimming  medusa  (jelly  fish) 
k,  the  body  (manubrium)  with  the  mouth  at 
its  tip;/,  the  surrounding  bell;  w,  radial  canal; 
«,  sense  organ;  so,  tentacle;  b  and  c,  after 
Allman. 


332 


GENERAL  BIOLOGY 


multiplied;  the  new  ones  growing  up  are  separated  parts  of 
that  one,  and  are  therefore  essentially  like  it. 

The  parts,  however,  are  not  necessarily  identical  with  the 
parent,  or  with  each  other;  when  separated  they  may 
develop  slight  differences,  as  in  the  well  known  phenomenon 
of  bud   variation,  and  such    differences  may  be  increased 


V 


Fig.    186.     Duckweed    (Spirodela     polyrhiza).     The     growth     from   a 
I,   single  plant  in  twelve  days.      Photo   and  culture  by   L.  S.  Hawkins. 

Note  the  grouping  in   pairs,  with   small   lobes   forming  between  the 

larger  old  ones  of  the  dividing  individuals. 

artificially  by  selection.  One  branch  of  a  rose  bush  may 
develop  finer  flowers  than  any  other  on  the  bush.  Cuttings 
of  this  branch  may  be  selected  for  growing,  and  the  best- 
flowered  shoots  developing  from  these  cuttings  may  be 
again  selected  with  some  advantage.  But  there  is  no 
probability  that  these  improvements  would  be  inherited. 


THE  LIFE  CYCLE  333 

The  special  means  by  which  individuals  multiply  them- 
selves asexually  are  far  too  numerous  and  diverse  for  us  to 
attempt  to  consider  them  all  here.  Stools  and  stolons  and 
runners  and  tubers  and  offsets  and  bulbs  and  a  dozen 
kinds  of  detachable  buds,  are  known  to  every  student  of 
plants.  Indeed,  many  of  those  plants  that  have  been  able 
to  advance  into  and  conquer  difficult  environments  and 
become  dominant  in  them,  (such  as  the  pond-weeds  on  the 
bottom  in  shoal  waters,  and  the  grasses  and  sedges  in  the 
fire-swept  prairies  and  marshes)  increase  mainly  asexually, 
by  extensions  of  the  plant  body.  They  still  produce  seeds, 
but  they  hold  their  ground  by  continuous  and  exclusive 
occupancy  of  it.  Budding  and  fragmentation  and  other 
such  methods  are  common  also  among  the  lower  animals. 
This  we  have  observed  in  the  hydra.  But  all  such  increase 
has  to  do  with  growth  as  well  as  with  reproduction.  Let  us 
here  consider  some  more  specialized  reproductive  parts  and 
methods,  that  are  more  exclusively  adapted  to  reproductive 
ends. 

Asexual  reproductive  cells. — When  these  are  formed  for 
dispersal,  they  are  usually  called  spores.  With  ordinary 
spores, as  they  are  com.monly  produced  upon  the  aerial  parts 
of  plants,  we  have  already  become  acquainted.  These  are 
minute  resting  cells,  usually  invested  with  a  protective 
covering  that  resists  evaporation,  and  that  permits  of  their 
being  distributed  by  currents  of  air. 

Among  aquatic  thallophytes,  both  algye  and  fungi,  there 
occurs  at  intervals  a  breaking  up  of  the  cell  contents  into 
minute  naked  unicellular  reproductive  bodies.  These  are 
called  zoospores  or  swarm  spores.  Each  zoospore  acquires 
two  or  four  flagella  (or  sometimes  a  circlet  of  cilia),  and, 
escaping  out  of  the  old  cell  wall,  it  swims  about  in  the 
water.  Finding  a  suitable  situation  it  attaches  itself  and 
begins  to  develop  a  new  plant  body  like  that  of  its  parent. 


334 


GENERAL  BIOLOGY 


The   alga   Draparnaldia,    shown     in   figure   187,     which 

grows  attached  to  stones  in 
the  riffles  of  small  clear-flow- 
ing permanent  streams,  and  is 
easily  seen  trailing  its  long 
beautifully  branching  fila- 
ments in  the  current,  is  a 
favorable  one  in  Avhich  to 
observe  zoospore  formation ; 
for  it  will  usually  develop 
zoospores  a  day  or  two 
after  being  brought  out  of  its 
native  environment  into  the 
laboratory.  The  spores,  escap- 
ing from  the  cells  singly,  will 
swim  to  the  lighted  side  of  the 
containing  vessel,  from  the 
surface  of  which  they  may 
often  be  obtained  in  great 
numbers. 
It  will  be  noticed  that  the  figure  of  the  zoospore  of  Drapar- 
naldia does  not  differ  materially  from  that  of  certain  of  the 
gametes  we  had  before  us  in  Chapter  II.  It  is  highly 
probable  that  sex  cells  were  developed  out  of  zoospores. 
Both  are  present  in  certain  algae,  and  are  hardly  to  be  dis- 
tinguished in  form ;  and  the  differences  between  them  almost 
vanish,  when,  as  sometimes  happens,  the  gametes  develop 
without  preliminary  fusion  in  pairs. 

Multicellular  reproductive  bodies. — In  certain  of  the 
lower  fresh  water  animals,  notably  in  sponges  and  bryo- 
zoans,  there  are  special  multicellular  reproductive  bodies 
called  statohlasts  (also  known  as  winter  buds,  and  gem- 
mules).  These  are  like  spores  only  in  function,  and  in  hav- 
ing resistant  walls  which  tide  them    over    the    dry,    hot 


Fig.  187.  Draparnaldia,  a,  a  "bit  of 
the  stem,  with  three  branches;  b, 
a  bit  of  a  branch  that  is  yielding 
zoospores. 


THE  LIFE  CYCLE 


335 


season     when      the    shoal   waters   in    which    they     grow 

*  evaporate.     While  they  are 

often  spoken  of  as  seed- 
like bodies,  they  are  wholly 
unlike  seeds  in  that  they 
contain  no  embryo,  and 
they  are  entirely  different 
in  origin.  During  the 
growing  season,  (spring  and 
early  summer) ,  little  groups 
of  cells  become  segregated 
within  the  tissues  of  the 
parent  animal  (fig.  i88y^), 
and  become  invested  there 
with  a  common  protective 
covering,  the  statoblast 
wall,  that  is  .  often  of  re- 
markably complicated  and 
beautiful  structure.  When 
the  parent  dies  and  its  flesh 
disintegrates,  the  stato- 
FiG.  188.    Piumateiiaa,  a  small  colony    blasts  are  liberated,    to  be 

growing    on    a    submerged    stick;  6,  a     ^prri^rl       Q'hrMi+        -ix^i-fV.       +V.o 
small    part    of  a    single   branch,   with     CarriCQ      aOOUt        Wltn       tnc 

cS«raido'„trinL"f'??nfe2f„'e"(U-   Waters,    Or    blown     about 
lo\\C^e*\?r?sf  of  SSsT;'  Ji    with  the  dust  of  the  dessi- 

esophagus;  n,  the  chitinous  sheath  that     r^c,+ar\    Kz-vf-f /^t->T     r>-iii^l      /^^      :^ 
shelters  an  individual,  (after  Allman)        caiCQ    DOCIOm    mUQ,     Or,     m 

the  case  of  statoblasts  pro- 
vided with  grappling  hooks,  such  as  those  of  Pectinatella, 
to  be  carried  and  distributed  by  aquatic  animals.  In  the 
Spring,  those  favorably  situated  germinate  and  develop  new 
colonies  of  the  parent  form. 

Statoblasts  occur  in  groups  most  of  whose  members  are 
marine.  They  are  probably  an  adaptation  of  the  life  cycle 
to    the    conditions  imposed    by    shoal  and     impermanent 


33^ 


GENERAL  BIOLOGY 


waters.      Not   all    the    sponges  and   bryozoans  that    live 
in  fresh  waters  are  known  to  produce  statoblasts,  but  the 

more  common 
shoal-water  forms 
produce  them  in 
very  great  abun- 
dance (fig.  189).  In 
early   summer   the 


freshly 


grown 


Fig.  189.  Freshwater  sponge  (Spongilla  fluviatilis) 
disintegrating  in  late  summer,  showing  the  abun- 
dant seed-like  statoblasts. 


sponges  may  be 
found  by  lifting 
and  overturning 
boards,  boughs,  or 
almost  any  solid 
support  that  pro- 
jects into  the  water, 
and  few  if  any 
statoblasts  will  be 
found;  but  in  late 
summer,  when  the 
sponge  fiesh  is  falling  away,  the  statoblasts  will  be  found 
in  patches  scattered  thickly  over  the  surface  as  minute 
rounded  yellow  bodies  about  the  size  of  small  mustard 
seeds.  These  may  be  germinated  after  a  resting  spell,  in 
a  watchglass,  the  numerous  amoeboid  cells  contained  in 
them  issuing  separately  from  a  side  pore  in  the  wall,  and 
then  soon  coming  together  to  form  a  delicate  chimney-like 
tube,  which  is  the  first  of  the  water  channels  of  the  new 
sponge,  and  out  of  the  summit  of  which  the  water  can 
very  early  be  seen  streaming.  Doubtless  it  is  in  this 
same  way  that  new  sponges  are.  started  in  the  sloughs 
each  spring.  Many  of  them,  doubtless,  remain  attached 
to  the  support  where  they  grew,  there  to  develope  a  new 
sponge  on  the  old  site. 


THE  LIFE  CYCLE 


337 


Study  40.     Observations  on  asexual  reproductive  methods. 

Materials  for  this  study  are  almost  limitless  in  number 
and  variety,  and  those  mentioned  below  are  suggested 
merely  as  types. 

Study  and  compare  together  a  few 
special  reproductive  bodies,  such  as  the 
"gemmules"  of  the  common  greenhouse 
liverwort,  Marchantia,  the  frond  bulbs  of 
,  the  bladder  fern  (Cystopteris  bulbifera) ,  the 
*^  "bulbils"  of  the  tigec  lily,  the  "sets"  of  the 
onion,  the  tubers  of  the  potato,  etc.,  etc. 

Study  the  swarm  spores  of  Drapernaldia 
(fig.  187),  or  of  Cladophora  (in  which  they 
are  produced  in  great  numbers  in  single 
terminal  cells),  or  of  any  of  the  water 
molds. 

Study  and  compare  together  the  stato- 
blasts  of  such  forms  as  Plumatella  and 
Pectinatella  among  bryozoans  and  of 
Spongilla  and  Heteromyenia  among  fresh 
water  sponges;  prepared  slides  will  prob- 
ably be  needed    for  this.     If  some  sponge 

Fig.  190.    Polv-  -^  .  h-       & 

embryonyin    statoblasts  can be  gcrmmatcd  under  obser- 

Po  lygnotus  .  . 

(after  Marchai).    vation,  their   multicellular   nature    will   be 

a,    the    egg;     b, 

the    same  after     apparent. 

repeated      divi-  r      1   • 

sions  of  its  nu  •        The  rccord   of  this    study   may   consist 

cleus;      c,     the 

same    after  the     m    nOtCS    On     and    llStS    of     the    objects    ex- 
development  of  .  .   1  ,  , 

separate  em-    ammcd,    together  with    sketches  of  some 


bryos  from  each 
of  the  parts  (de-  of  them 
tails  indicated 
diagramm  a  t  i  - 
cally  in  but  two, 
and  these  at  dif- 
ferent stages  of 
progress) . 


Polyembryony. — This  is  another  kind  of 
asexual  method  of  increase,  that  is  even 
more  different  in  kind  from  the  two 
preceding  than  they  are  from  each  other.  In  certain 
parasitic    insects    of    the    order    Hymenoptera,    the  eggs 


238  GENERAL  BIOLOGY 

which  are  laid  within  the  soft  and  richly  nourished 
larvae  of  other  insects,  undergo  a  division  which  is 
rather  fragmentation,  than  segmentation;  for  it 
results  in  the  development  not  of  a  single  embryo  but 
of  many  embryos.  The  parts  into  which  the  nucleus 
divides  develop  separately  as  indicated  diagrammatically 
in  figure  190,  each  becoming  a  complete  embryo,  and 
growing  later  to  adult  estate.  A  significant  feature  of  de- 
velopment by  this  method  is  that  all  the  individuals  de- 
veloped from  one  egg  are  of  the  same  sex. 

Reproductive  methods  in  general. — Sufficient  illustrations 
have  now  been  before  us  to  show  that  there  is  one  sexual 
method  of  reproduction,  fairly  uniform  and  consistent 
throughout  the  organic  world,  but  that  there  are  many 
asexual  methods,  and  that  these  latter  are  most  diverse. 
The  former  is  uniform  in  its  fundamentals  in  all  kinds 
of  environment;  the  latter  are  uniform  in  nothing,  and  they 
show  the   most   significant   relations  to  conditions  of  life. 

The  unity  of  the  organic  world  is  hardly  more  manifest 
in  the  possession  of  protoplasm,  than  in  the  production  of 
gametes,  and  in  the  fusion  of  these  in  fertihzation.  The 
primary  differentiation  of  multicellular  bodies  is  into  germ 
plasm  and  body  plasm.  This  is  even  older  than  the 
differentiation  between  plants  and  animals.  But  the 
secondary  sexual  characters  show  as  great  diversity  as  do 
asexual  reproductive  phenomena:  these  are  the  after 
thoughts  of  reproduction:  these  are  the  special  means 
adopted  by  special  groups.  How  different  are  even  sperm- 
aries  and  ovaries  in  the  stoneworts  and  in  the  liverworts ! 
How  lacking  in  common  features  are  the  reproductive  organs 
of  an  earthworm  and  a  salamander !  All  these  have  been 
more  recently  developed,  along  independent  lines,  in  accord- 
ance with  the  tendencies  and  in  adaptation  to  the  needs 
of  the  different  groups  in   which  they  are  found. 


THE  LIFE  CYCLE  339 

The  principal  relations  that  the  sexual  and  asexual 
methods  may  bear  to  each  other  are  diagrammatically 
indicated  in  figure  191.  Six  generations  are  represented 
in  the  six  vertical  columns.  A  small  circle  represents  the 
egg;  a  dash  with  a  tail,  the  sperm;  a  circle  inclosing  a  dot, 
the  zygote;    the  black  dots    are    spores,    and    the    black 


6 


6 


(S-.-.  6^-.  (f— .  (5:--  6-- 


Fig.  191.  Diagram  of  types  of  reproduction;  /,  normal  sexual  reproduc- 
tion; 2,  parthenogenesis;  j,  alternation  of  generations;  ,?,  polyembryony,  etc.; 
J,  occasional  production  of  sex  cells  in  a  series  of  spore  forming  individuals; 
6,  continuous  spore  formation. 

dashes  are  egg  fragments.  The  top  line  of  figures  repre- 
sents ordinary  sexual  reproduction,  occurring  alone,  sub- 
stantially as  previously  shown  in  figure  174.  The  second 
line  represents  parthenogenesis  (with  only  three  genera- 
tions of  females  included  between  the  bisexual  generations'^). 


*In  most  parthenogenetic  species,  the  sexual  generations  recur 
at  much  greater  intervals.  In  fact,  in  certain  species  of  rotifers 
and  also  in  certain  gall  wasps  (Cynipidae)  no  males  are  known, 
and  parthenogenetic  reproduction  appears  to  be  continuous.  On 
the  other  hand  in  one  genus  of  gall  wasps  (Neuroterus)  single 
sexual  and  parthenogenetic  generations  regularly  alternate;  and, 
strangely  enough,  the  females  of  the  latter  differ  so  much  in  form 
and  structure  from  the  former  that  they  have  been  described  as 
a  diiferent  genus  (Spathegaster). 


340 


GEXERAL  BIOLOGY 


The  third  line  represents  alternation  of  generations,  as  we 
have  studied  it  among  the  higher  plants ;  substitute  buds  for 
the  spores,  and  it  would  represent  equally  well  alternation 
of  hydranth  and  medusa  in  the  hydroids.  The  fourth  line 
represents  polyembryony,  as  just  described.  It  also  repre- 
sents the  conditions  found  in  the  alga  Coleochete,  in  which 
the  fertilized  egg  breaks  up  into  eight  zoospores,  each  of 
which  then  develops  an  independent  bisexual  plant.  The 
fifth  line  represents  the  production  of  sex  cells  upon 
occasional  members  in  a  series  of  spore-bearing  plants. 
This  occurs  in  Mucor  and  other  molds.  The  last  line 
represents  continuous  spore  formation,  and  entire  absence 
of  sexual  reproduction — a  condition  that  is  believed  to  pre- 
vail in  some  of  the  green  algae. 

III.       CHANGE     OF     FORIM     WITH    ALTERNATION      OF    HOSTS. 

Among  the  shifts  that  organisms  make  for  a  place  and  a 
living  on  the  earth,  none  are  more  remarkable  than  those 


Fig.   192.     The  witch  hazel    pocket -gall  aphid    (Rormaphis   hamamelidis)    a 
young  larva;  b,  grown  larva;  c,  adult     (after  Pergande). 


THE  LIFE   CYCLE 


341 


of  parasites  from  one  host  to  another;  and  there  are  some 
remarkable  changes  of  form  accompanying  the  shifts.  For 
example,  the  witch  hazel  aphid(fig.  i92)that  causes  the  con- 
ical mantle  galls(shown  at  fig.  326)  upon  the  leaves,  and  that 


a 


Fig.    193.     The  same  aphid  shown  in  figure  192,  In  the    form    assumed    after 
migration  to  the  birch,     a,  dorsal,  6,  ventral,    and    c,  lateral    views   of    the 
adult  (after  Pergande). 

grows  up  inside  them,  is  of  the  ordinary  form  of  the  common 
aphids  during  its  life  within  these  galls  (two  generations). 
But  in  midsummer,  when  its  food  supply  begins  to  be  cut 
off  by  the  drying  up  of  the  galls,  it  migrates  to  a  new  host 
plant.  It  flies  through  the  air  in  search  of  birch  trees,  and 
finding  them,  settles  upon  the  under  side  of  the  leaves  to 
dwell  there  the  remainder  of  the  season.  There  it  gives 
birth  to  numerous  young,  which  will  grow  up  for  three  suc- 
cessive generations  into  the  adult  form  shown  in  figure  193. 


342 


GENERAL  BIOLOGY 


In  autumn  the  descendants  of  these  will  grow  into  an  adult 
form  very  like  that  shown  in  the  first  figure  (fig.  192),  and 
will  fly  back  to  the  witch  hazel,  and  the  young  of  these 
developed  upon  the  witch  hazel  will  be  wingless  males  and 
females,  all  the  other  generations  through  the  year  having 
consisted  of  females  alone.  There  are  other  minor  differ- 
ences, none  of  the  seven  generations  of  the  season  being 
exactly  alike  either  in  adult  form  or  in  developmental 
stages;  but  the  two  forms  shown  in  the  figures  are  certainly 
so  different  they  would  not  be  thought  to  be  one  and  the 
same  species  by  any  one  who  did  not  know  their  life  history. 

Other  cases  of  change  of  form  with  alternation  of  host  are 
well  known ;  probably  they  are  more  numerous  than  we  now 
realize,  because  of  the  great  difficulty  of  recognizing  the 
identity  of  the  different  forms.  The  best  known  are  perhaps 
among  animals  the  liver-fluke  of  the  sheep  (whose  host  ani- 
mals are  the  sheep  and  the  snail ;  an  account  of  it  may  be 
found  in  almost  any  general  text  book  of  zoology) ;  and 
among  plants,  the  wheat  rust  (whose  host  plants  are  wheat 
and  barberry ;  an  account  of  it  may  be  found  in  almost  any 
text-book  of  botany). 

We  will  now  leave  these  cases  of  heteromorphic  adult 
organisms,  which  though  striking  are  rather  rare  and  in- 
consequential, and  consider  the  far  more  common  form- 
changes  that  occur  in  the  life  time  of  single  individuals. 

IV.      METAMORPHOSIS. 

This  is  the  name  applied  to  changes  of  form  undergone 
after  the  close  of  embryonic  Hfe — ordinarily,  after  hatching 
from  the  egg.  These  changes  may  be  inconsiderable,  as 
in  the  earthworm,  or  the  leech  (fig.  194),  but  in  a  number  of 
the  higher  groups  of  animals  they  are  so  great  that  the 
young  of  many  forms  were  originally  described  as  inde- 
pendent organisms,     and    given   separate     names.      Thus 


THE   LIFE   CYCLE 


343 


arose    the    names    still    borne  by  the    nauplius  and  zoaea 
stages     of     post-embryonic    development    in    crabs,    the 

leptocephalus  stage  of  eels, 
etc.  We  have  seen  that  there 
is  something  of  a  transfor- 
mation occurring  in  the  sala- 
mander at  the  beginning  of 
its  adult  life,  and  a  still 
greater  one  in  the  frog,  when 
gills  and  tail  are  lost,  new 
mouth-parts  are  acquired  and 
the  lungs  become  functional. 
Indeed,  we  should  not  fail  to 
recognize  a  sort  of  transfor- 
mation in  ourselves  during 
our  earlier  years,  when  our 
first  set  of  teeth  drop  out 
and  we  develop  another  and 
larger  one ;  and  in  other 
changes  that  occur  later,  in 
adolescence.  But  the  most 
remarkable  examples  of  meta- 
morphosis, as  well  as  the  most 
available  for  study,  are  found 
among  insects,  and  these  will 
serve  us  for  illustration  of 
this  phenomenon. 
The  transformations  of  insects.— In  all  of  the  winged 
insect  groups  there  is  a  considerable  change  of  form  at  the 
time  of  entrance  upon  adult  life. 

When  these  changes  are  least,  as  in  the  grasshopper  (fig. 
195),  the  wings  are  expanded  and  the  reproductive  organs, 
perfected;  when  they  are  greatest,  every  part  of  the  body  is 
refashioned,  and  the  larva  bears  hardly  any  resemblance  to 


Fig.  194.  Leech  (Clap  sine) 
overturned,  showing  the  brood 
of  young  protected  beneath  the 
body. 


344 


GENERAL    BIOLOGY 


the  adult.  In  the  former  case,  there  are  but  two  stages  of 
metamorphosis,  following  hatching,  the  nymph*  (fig.  196) 
and  the  adult   (imago).       In  the  latter,  there  are  three: 


Fig.  195.     An  adult  grasshopper. 


larva,  pupa  and  adult.     When  the  differences  between  the 
larva  and  adult  become  so  great  that  rapid  change  from 


'> 


w> 


Fig.  196.     A  grasshopper  nymph,  well  grown. 


♦Larva  is  a  general  term,  covering  all  sorts  of  immature  stages, 
each  of  which  bears  a  separate  designation  in  nearly  every  one  of 
the  major  groups  of  animals:  nymph  is  the  name  for  one  sort  of 
larva  in  insects — the  sort  that  is  most  easily  recognized  by  its 
externally  developing  wings. 


THE    LIFE    CYCLE 


345 


one  to  the  other  is  incompatible  with  the  ordinary  use  of 
the  organs,  the  quiescent  pupal  stage  comes  in  as  a  transi- 
tion stage,  a  period  of  making  over,  during  which  the  neces- 
sary extensive  alterations  of  the  body  are  effected      The 


J 


Fig.  197.     The    larva  of    a    diving    beetle     (Hydroporus 
undulatus) . 

pupal  stage  is  peculiar  to  insects,  and  its  presence  or 
absence  within  the  group  distinguishes  between  the  so-called 
'.'complete"  and  "incomplete"  metamorphosis. 


Fig.  198.  The  pupa  of  the 
same  diving  beetle  (drawn 
by  Miss  Helen  V,  William- 
son). 


— -< 


Fig.  199.  The  adult  diving 
beetle  (Hydroporus  undu- 
latus). 


346  GENERAL  BIOLOGY 

Study  41.     External  metamorphosis  in  insects. 

Materials  needed:  Two  selected  examples  illustrating 
the  two  main  types  of  insect  metamorphosis,  preferably 
living  and  actively  transforming  in  the  laboratory;  i)  nymphs 
and  adults  of  a  grasshopper,  a  mayfly  or  a  stonefly,  and 
2)  larvae,  pupae,  and  adults  of  mosquitoes,  or  meal-worms  or 
bean  weevils,  or  any  other  easily  managed  forms  (see 
appendix). 

Also  nymphs  and  adults  of  the  following  in  alcohol: 
grasshoppers,  (Orthoptera) ;  psocids,  (Corrodentia) ;  stone- 
flies,  (Plecoptera) ;  mayflies,  (Ephemerida) ;  dragonflies, 
(Odonata) ;  bugs,  (Hemiptera) :  and  larvae  and  adults  of 
any  Neuroptera,  Trichoptera  or  Mecoptera,  of  Lepidoptera, 
of  Coleoptera  (a  weevil,  and  a  larva  with  legs) ,  of  Hymenop- 
tera  (a  sawfly  and  a  bee  or  ant)  and  of  Diptera,  (mosquito 
or  cranefly  or  other  nematocerous  larva,  and  one  of  the 
degenerate  housefly  or  fleshfly  type). 

Prepare  a  table  with  the  following  column  headings, 
abbreviated  as  desired : 

1.  Name  of  insect. 

2.  Order  to  which  it  belongs. 

3.  Relative   size  of  head,  thorax  and  abdomen, 
expressed  in  the  ratio  i  :x:y. 

4.  Skin  (thick  or  thin,  hairy  spiny  or  naked,  etc.) 

5.  Eyes  (well-  or  ill-developed,  large  or  small). 

6.  Antennae  (relative  development) . 

7.  Mouth  parts  (adapted  for  biting  or  sucking,  or 
vestigial) . 

8.  Wings  (externally  or  internally  developing). 

9.  Legs  (relative  development). 

10.  Peculiar  parts  (parts  found  in  this  larva  only). 

11.  Lives  where. 

12.  Eats  what. 


u 

C 

> 

Oj 


< 


THE  LIFE  CYCLE  347 

13.  Relative  size  of  head,   tliorax  and  abdomen, 
expressed  in  the  ratio,  /  -.x-.y. 

14.  Antennse  (relative  development.) 

15.  Mouthparts  (adapted  for  biting  or  sucking,  or 
atrophied). 

16.  Legs,  (relative  development). 

17.  Lives  where. 

18.  Eats  what. 

Write  the  forms  in  this  table  (by  groups)  in  the  order 
of  their  departure  from  primitive  similarity  between  larva 
and  adult.  Fill  out  the  table.  Then  study  it,  and  read 
out  of  it  the  story  it  contains  of  the  divergence  of  larval 
and  adult  stages,  and  in  the  last  two  columns  under  both 
larva  and  adult,  see  how  this  divergence  is  correlated  with 
change  of  manner  of  life. 

The  internal  metamorphosis  of  insects. — While  there  is 
no  pupal  stage  in  insects  of  incomplete  metamorphosis, 
such  as  the  mayfly  (fig.  200) ,  there  is  a  corresponding  period 
just  before  transformation  during  which  the  full  grown 
nymph  is  quiescent  for  a  short  time,  and  during  which  there 
is  rapid  growth  of  wing  muscles  and  of  other  internal 
organs;  and  some  pupae,  like  those  of  the  mosquitoes,  caddis 
flies  and  the  true  Neuroptera,  are  not  wholly  quiescent. 
But  in  the  pupas  of  all  the  more  specialized  forms,  besides 
the  development  of  new  tissues,  there  is  going  on  a  de- 
struction of  old  ones  that  are  not  suited  to  the  needs  of  the 
adult  and  a  reconstruction  of  their  materials  in  new  form. 
The  pupal  stage  thus  becomes  one  of  peculiar  helplessness 
in  the  life  of  the  insect  and  it  is  spent  in  the  shelter  and 
seclusion  of  a  pupal  cell  or  burrow  or  cocoon.  Larval 
life  is  abbreviated.  The  larva  stores  fat  rapidly,  and 
in  relatively  large  quantity,  postponing  the  final  elabora- 
tion of  it  into  organs.     And  the  amount  of  fat  in  its  body 


34S  GENERAL  BIOLOGY 

is  more  or  less  proportionate  to  the  extent  of  the  changes 
to  be  made  during  transformation.  The  advantage  of  this 
lies  in  the  ability  of  such  an  insect  to  avail  itself  of  a  rich 
but  transient  food  supply.     A  generation  may  be  reared 


Fig.  200.  Adult  and  nymph  of  the  mayfly  Calli- 
baetis  skokiana  (drawn  by  Miss  Maude  H. 
Anthony). 

on  the  fallen  carcass  or  the  ripe  fruit  before  it  is  decom- 
posed, or  in  the  rich  endosperm  of  the  developing  seed 
before  it  has  hardened. 


THE   LIFE   CYCLE 


349 


Fig.  201.  Metamorphosis  in  the  iris  weevil  (Alononychus  vulpeadns)  m,  the 
larva  at  the  beginning  of  transformation;  /,  leg  buds  and  it;,  wing  buds, 
showing  through  the  translucent  skin. 

n,  longitudinal  section  of  a  leg  bud  of  the  larva,  showing  three  principal 
divisions:     /,  the  remains  of  fat  cells;    /,  leucocytes. 

o,  vertical  section  through  the  wing  bud  of  the  larva;  w,  the  point  of  the  wing 
that  is  to  be,  with  a  shelf  of  epidermis  projecting  below  it;  c,  the  loosened 
cuticle;  /,  fat;  m,  muscle;   t,  air  tube  (trachea). 

p,  Cross  section  of  a  larva  just  before  its  final  transformation  to  a  pupa: 
w,  wing  and  I.  leg  are  now  exserted,  and  the  latter  .shows  differentiation  into 
femur  tibia  and  tarsus;  k,  stomach;  e,  digestive  epithelium;  n,  doublenerve 
cord;  dv,  dorsal  blood  vessel;  /,  whole  fat  and  o,  o,  o,  dissolving  fat;  w,  new 
muscle  fibres  forming. 


3  5^^ 


GENERAL   BIOLOGY 


This  destruction  of  larval  tissues  during  the  pupal  stage  is 
one  of  the  most  remarkable  deviations  from  the  ordinary 
progressive  course  of  the  life  cycle.  Similar  processes  occur 
wherever  larval  organs  are  to  be  made  over.  The  tadpole's 
tail  does  not  drop  off;    that  would  be  a  waste  of  valuable 

organic  materials.  It  is 
reabsorbed:  i.  e.,  it  is  dis- 
solved and  transported 
and  used  again  for  the 
building  of  other  parts. 
The  agents  of  the  reabsorp- 
tion  in  the  tadpole  are 
leucocytes  that  have 
turned  temporarily  to  a 
diet  of  muscle  fibres  (and 
are  called  during  their  tis- 
sue-eating period,  phago- 
cytes: the  phenomenon  is  called  phagocytosis  see  fig.  202). 


Fig.  202.  Phagocytosis  in  the  fat  of  the 
abdomen  of  the  ins  weevil.  /,  fat; 
p,  phagocytes. 


Some  of  the  tissues  of  the  insect  larvae  are  eaten  and 
transported  by  phagocytes.  Others  appear  to  be  self  dis- 
integrating; their  nuclei  divide  extensively  and  become 
very  small  and  then  gather  about  themselves  the  reinte- 
grated remains  of  the  old  cytoplasm  and  of  dissolved  fat 
cells,  and  fashion  them  into  new  cell  bodies,  often  constitut- 
ing organs  of  very  different  form  in  the  adult.  The  process 
is  somewhat  like  a  return  to  an  embryonic  condition, 
followed  by  a  new  embryonic  development,  wherein  the 
fat  of  the  larva  stands  in  the  stead  of  the  yolk  in  the  egg. 
If  at  the  height  of  metamorphosis  one  cut  open  a  pupa 
that  has  developed  from  any  of  the  more  degenerate  larvae, 
he  finds  little  semblance  of  organs,  the  greater  part  of  the 
body  being  reduced  to  a  fluid  mass  which  flows  ovit  at  every 
cut. 


THE  LIFE  CYCLE 


35i 


Not  all  of  the  body  is  thus  destroyed,  however;  there  are 

preserved  little  islands  o 
regenerative  cells  in  all  the 
principal  parts  of  the  body 
from  which  their  respective 
continents  will  be  reformed. 
In  the  walls  of  the  stomach, 
for  example, there  are  grouped 
rings  or  masses  of  little  cells, 
rich  in  protoplasm,  by  which 
the  new  epithelium  of  the  new 
stomach  will  be  developed. 
The  undeveloped  legs  and 
wings  exist  in  the  larva  as 
little  buds  of  active  cells,  at- 
tached to  the  inner  face  of  the 
body  walls.  From  these  legs 
and  wings  now  grow  out,  at 
first  beneath  the  larval  skin,  to 
be  freed  at  its  last  moulting. 
About  the  bases  of  these 
organs  and  from  other  regen- 

FiG.    203.      Cone    galls    of   'the    willows     f^rufUrn  ppH   maccpc  in   +V.e  -ixroll 
caused  bv  the  gall  midge  Rhabdophaga     eraXlVC  CCU  maSSCS  m  tHC  Wall 

y/od'S^Sn  ^SaiL^^di^c^o^Srl.  fhe    itsclf,   the  new  body  wall   is 
bebtiana.^""^  ^^^^  produced  on  Saiix    developed.     Details   of  thcse 

wonderful  processes  may  not 
be  studied  here,  but  there  are  some  easily  observable  phe- 
nomena, which  will  help  us  to  understand  the  main  points. 

Study  42.     Observations  on  internal  metamorphosis. 

Materials    ne<^^ed:     Living    larvae    and    pupae    of    some 
dipterous  species  having  red  blood* ;  preferably  of  the  cone 


*The  blood  of  insects  is  not  red,  except  in  a  few  forms,  such  as 
the  so-called  "blood  worms",  that  are  the  larvae  of  midges  (Chir- 
on omidae),  and  in  some  of  the  larvae  of  gall  midges  (Cecido- 
myidae). 


352  GENERAL  BIOLOGY 

gall  midge  of  the  willow,  (fig.  203)  in  abundance  (see  appen- 
dix) .  Prepared  cross-sections  of  the  thorax  of  old  larvae 
showing  wing  and  leg  buds.  Cross  sections  of  the  thorax  of 
a  damsel  fly  for  comparison  of  fat  development. 

The  central  cavity  of  the  gall  may  readily  be  exposed  by 
sinkine  the  end  of  a  knife  blade  or  scalpel  lengthwise 
through  the  end  of  the  stem  in  the  base  of  the  gall,  and 
twisting  laterally,  laying  it  open.  Although  the  blood  is 
red,  the  grown  larva  will  appear  white,  because  it  is  filled 
with  opaque  white  fat.  As  the  dissolution  of  the  fat  pro- 
ceeds the  red  color  of  the  blood  will  reappear.  The  progress 
of  the  pupa  in  metamorphosis  may,  therefore,  from  the 
first  be  gauged  by  the  extent  of  the  red  color;  later,  as  the 
end  of  the  pupal  period  approaches,  the  black  pigmentation 
of  the  adult  w^ill  gradually  overspread  the  surface,  beginning 
with  the  eyes. 

Sketch  the  pupa  in  outline,  and  make  several  rapid  copies 
of  the  sketch  by  tracing.  Then  color  these  with  red  and 
black  pencils  (or  with  water  colors,  if  preferred)  to  indicate 
the  external  evidence  of  the  internal  changes.  Show  thus 
the  place  of  beginning  and  the  order  of  progression  in  fat 
solution,  and  later  progress  in  pigmentation. 

Place  a  live  pupa  that  is  in  the  midst  of  metamorphosis  on  a 
hollow^  ground  slide  in  a  drop  of  normal  salt  solution,  and 
split  it  lengthwise  w4th  fine  scissors.  Gently  wash  away 
the  dissolved  interior  with  a  little  stream  of  normal  salt 
solution  from  a  fine  pipette  and  examine  carefully  the  extent 
and  the  appearance  of  the  solid  organs  remaining.  A  like 
treatment  of  a  larva  Avould  disclose  the  wing  buds  and 
leg  buds  appended  to  the  interior  of  the  body  wall. 

Study  and  diagram  a  section  of  the  thorax,  showing  wing 
and  leg  buds;  show  also  the  proportion  of  fat  and  solid  tis- 
sue; compare  this  with  cross  section  of  thorax  of  a  damselfly. 

The  record  of  this  study  will  consist  in  the  drawings  and 
diagrams  suggested  above. 


THE    LIFE  CYCLE  353 

V.      ARTIFICIAL   DIVISION   AND   COMBINATION    OF   ORGANISMS. 

In  the  arts  of  men,  artificial  division  for  increase  of 
organisms  asexually  and  artificial  combination  of  the  parts 
of  two  organisms  for  the  purpose  of  temporarily  combining 
their  characters  in  one  individual,  have  long  been  success- 
fully practiced.  The  former  is  known  in  the  gardener's  art 
as  artificial  propagation;  the  latter,  as  grafting.  The  parts 
of  an  organism  that  are  to  grow  up  into  separate  whole 
organisms  must  contain  cells  sufficiently  undifferentiated 
either  to  be  able  to  redevelop  the  missing  parts,  or  to  re- 
shape them  out  of  pre-existing  tissues.  The  parts  of  two 
organisms  that  are  to  be  organically  joined  together  must 
contain  cells  sufficiently  plastic  and  formative  to  be  able 
to  effect  organic  union  between  the  conjoined  parts. 

Regeneration.— The  artificial  propagation  of  the  gardener 
is  called,  when  practiced  by  the  zoologist,  regeneration;  and 
this  name  embodies  the  essential  phenomena  involved — the 
redevelopment  of  the  missing  parts  of  a  piece  of  an  organ- 
ism. The  slip  cut  from  the  top  of  an  old  geranium  lacks 
roots,  and  when  placed  in  wet  sand  in  a  window  box,  it 
develops  a  new  root  system  out  of  the  undifferentiated  tis- 
sues of  its  base,  and  does  not  proceed  much  further  with 
leaf  development  until  roots  are  established. 

The  capacity  for  regenerating  missing  parts  varies  much 
in  different  organisms.  It  is  very  great  in  most  plants,  and 
in  many  of  the  lower  animals;  but  it  is  so  poor  in  ourselves, 
that  after  we  reach  adult  life  we  may  hardly  replace  a  patch 
of  skin  well  enough  to  avoid  a  permanent  scar.  If  the 
tentacle  of  a  hydra  be  cut  off,  another  promptly  grows 
from  the  base  of  the  old  one.  If  the  body  be  cut  in  two,  two 
perfect  hydras  develop  from  the  parts,  a  new  foot  being 
formed  on  the  one  and  a  new  head  on  the  other.  Indeed, 
the  body  may  be  cut  into  many  pieces,  and  each  piece  that 


354 


GENERAL  BIOLOGY 


contains  the  fundamental  tissues,  in  such  relation  that  food 

can  be  taken,  may,  under  favorable  con- 
ditions, develop  into  a  perfect  hydra.  A 
single  arm  broken  from  a  starfish  will 
regenerate  the  body  and  all  the  other 
arms.  But  as  we  ascend  the  scale  of 
animal  life,  the  power  of  regeneration 
becomes  more  limited  as  organization 
becomes  more  complex  and  the  adjust- 
ment between  the  organs,  more  delicate. 
Herein  lies  one  of  the  limitations  of 
specialization  already  mentioned  (page 
251).  Blood  vessels,  for  example,  are 
excellent  agents  of  circulation  when 
intact,  but  when  cut,  they  wonderfully 
facilitate  bleeding  to  death.  Planarians 
(fig.  204)  are  classical  subjects  for 
regeneration  experiments.  They  may 
be  cut  to  pieces  apparently  without  very 
serious  inconvenience,  and  regenerate 
missing  parts  with  great  readiness. 
They  have  no  parts  that  can  be  put 
entirely  out  of  commission  by  being 
severed.  They  have  no  blood  vessel 
system,  nor  organs  of  respiration.  They 
have  a  sort  of  brain,  but  it  is  of  so  little 
consequence  that  when  the  head  containing  it  is  cut  off, 
another  one  is  promptly  grown.  The  other  organs  all 
appear  equally  well  adapted  to  withstand  mishaps.  The 
extraordinary  food  canals,  branching  and  ramifying  all 
through  the  tissues,  supply  with  a  food  receptacle  even  the 
smallest  piece  of  the  body  that  may  readily  be  severed. 
Figure  206  shows  the  regeneration  of  the  two  halves  of  a 
planarian  that  was  cut  in  two  in  the  median  plane  of  the 


Fig.  204.  Diagram  of 
a  planarian,  showing 
food  cavity  in  gray 
and  central  nervous 
system  in  black,  tn, 
mouth  at  the  end  of 
a  cylindric  pharynx 
that  is  directed 
downward. 


THE  LIFE  CYCLE 


355 


body — a  division  that,  as  every  one  knows,  would  be  in- 
stantly fatal  to  any  of  the  higher  animals.  Most  arthropods 
regenerate  lost  appendages  readily,  but  slowly,  the  new 
appendage  increasing  in  size  a  little  at  every  moult.  The 
crawfish  (and  many  of  its  allies)  is  so  provided  against  the 
loss  of  its  legs  that  a  special  breaking  place  is  developed 
across  the  middle  of  the  second  joint  in  them,  a  groove  across 
the  joint,  and  folds  of  membranes  wdthin  it,  that  prevent 


T 


g\j' 

Fig.  205.  Regeneration  in  Planaria  (a  to  g  after  Morgan;  h, 
after  Voigt).  a,  a  planaria  that  was  divided  as  indicated 
along  the  median  line  of  the  body,  b,  c,  d,  the  regeneration 
of  the  left  half,  that  was  fed.  e,  f,  g,  the  regeneration  of  the 
other  half  that  had  no  food,  h,  regeneration  of  pieces 
obliquely  cleft  partly  free  from  the  body:  at  x  a  new  tail 
and  at  y  a  new  head  and  at  z  both  a  new  tail  and  a  new  head 
have  appeared. 

excess  of  bleeding  when  the  leg  breaks  off.  Specimens  are 
collected  not  infrequently,  having  one  of  the  big  claws 
much  smaller  than  the  other,  and  in  process  of  regeneration; 
a  crawfish,  seized  by  one  of  the  big  claws  will  sometimes 
automatically  cast  it  off  and  escape  without  it.  Indeed, 
so  readily  are  the  big  claws  of  the  related  fiddler  crabs  cast 
off,  that  in  handling  the  crabs  one  may  hardly  touch  the 
claws  without  inviting  their  loss. 


356 


GENERAL  BIOLOGY 


Normal  regenera- 
tion for  the  main- 
tenance   of  the  body. 

— Regeneration  o  f 
lost  parts  is  but  a 
manifestation  of  the 
power  of  growth  ap- 
plied  in  abnormal 
circumstances.  It  is 
a  very  noticeable 
thing  when,  by  some 
mishap  with  tools  or 
machinery,  we  knock 
off  a  finger  nail  and 
have  to  grow  a  new 
one;  but  physiologi- 
cally it  is  not  very 
different  from  getting 
our  hair  cut  and  hav- 
ing it  grow  out  again. 
Our  epidermis  is  con- 
tinually being  shed 
from  the  surface  and 
new  cells  are  con- 
tinually growing  up 
from  below.  An  ex- 
cellent example  of  the 
renewal  of  tissues 
inside   the    body    is 

Fig.  206.     Growth  of  digestive  epithelium  in  a  dragonfly  nymph    (Gomphus). 

a,  the  aUmentary  canal  as  a  whole;  g,  gill  chamber,  /and  2,  Main  divisions  of 
the  intestine,    x,    nephridia    (Malpighian  tubules)  :v,  stomach,   s,  crop. 

b,  Section  of  a  bit  of  the  stomach  wall:  k,  digestive  epithelium.  /,  longi- 
tudinal muscle  fibres;  m,  longitudinal  muscle  layer;  n.  (as  in  all  the 
following)    a  nest  of  cells  for  replacement  of   the  functional  epithelial  cells, 

c,  the  same  as  6,  after  fasting  two  weeks:  note  the  accumulation  of  di- 
gestive secretion  as  shown  in  height  of  functional  cells. 

d,  a  dissociation  preparation  of   part  of  one  of  the  replacement  cell  nests. 

e,  the  discharge  of  the  digestive  secretion  after  feeding,  o,  and  p,  globules 
of  discharge:  the  oldest   of  the  functional  cells   are  thus  thrown  off  bodily. 

f,  the  replacement  of  the  discharged  cells  with  new  ones   from    the  cell  nests 

n,  n,  n.     Note  the  new  (clear)  cells  crowding  to  the  surface. 


THE   LIFE  CYCLE  357 

furnished  by  the  digestive  epithelium  of  the  dragonfly  shown 
in  figure  206.  New  cells  are  constantly  being  formed  in 
little  replacement  centres  at  the  base  of  the  epithelial  layer, 
and  the  old  ones,  charged  with  the  digestive  secretions,  are 
thrown  off  at  every  meal,  to  be  mixed  with  the  food  and  by 
their  action  upon  it  to  dissolve  it. 

The  tissues  of  the  body  differ  much  in  their  capacity  for 
cell  replacement;  some  cells  like  those  of  the  lowermost 
layer  of  the  epidermis,  retain  this  capacity  through  life, 
others  like  nerve  cells  do  all  their  dividing  in  embryonic  life 
(hence,  the  great  size  to  which  the  brain  of  the  higher  verte- 
brates so  early  attains),  and  have  no  capacity  for  making 
good  cell  losses.     But  if  they  have  lost  the  power  of  produc- 


'/Do  ©.■©/  U 

Fig.  207.  Diagram  of  cell  regeneration  (after  Morgan). 
a,  an  egg  of  a  sea  urchin  that  was  divided  as  shown  by 
the  oblique  line;  b  to  f  its  subsequent  development; 
g,  the  enucleate  part  of  the  egg;  h,  its  fertilization  by  a 
sperm  cell;  i,  j,  k,  its  subsequent  development. 

ing  new  cells,  they  retain  the  power  of  repairing  the  old 
ones.  If  a  nerve  fibre  be  severed,  a  new  fibre  may  grow  out 
from  the  cell  body  at  the  stump  of  the  old  one.  It  is  thus 
that  a  limb  regains  sensitiveness  after  being  paralyzed  by 
the  cutting  of  a  nerve. 

Regeneration  in  cells  and  in  embryos. — If  an  egg  cell  be 
divided  the  portion  containing  the  nucleus  may  reshape 
itself,  and  go  on  developing  quite  normally,  as  illustrated  in 
figure  207  b  to  /.  And  if  the  other  part  of  the  cytoplasm 
be  supplied  with  a  nucleus,  as  by  the  addition  of  a  sperm 
cell  of  the  same  species  (fig.  207  h)  it  also  may  develop  in 
the  ordinary  way.  The  two  cells  resulting  from  the  first 
division  of  the  egg  of  a  sea  urchin  may  develop  as  indicated 


358 


GENERAL  BIOLOGY 


a 


in  figure  208,  producing  two  individuals  of  half  the  usual 
size.     At  first  they  are  likely  to  develop  as  half  embryos, 

each  cell  and  its  descendants  behaving 
as  though  the  other  were  present.  Con- 
sequently the  blastula  when  formed  is 
open  on  one  side ;  but  it  closes  and  forms 
a  normal  embryo  later. 

In  most     bilateral  animals    the    first 
cleavage    plane    lies    in    the    medium 
plane  of  the  body  that  is   to  be,  and 
doubtless,  when   the  two    cells  remain 
together  each    develops   its  own  half  of 
the  body,  left  or  right;    but   the  above 
experiment  shows  that  either  is  capable 
of  developing   any  part  of    the   body. 
Frogs  eggs,  with  one  cell  killed  at    the 
two-cell  stage,  likewise   develop  at  first 
half  embryos,  which  later  become  whole 
ones.  Wilson  long  ago  showed  that  each 
of  the  cells  of  the   developing  lancelet, 
isolated     at  the     4-cell    stage    is  capa- 
ble of    forming    an  embryo,  but   at  the 
Fig    208    The    de-    ^-ccll    Stage,     cach    ccll    may     develop 
emb?>"irin*divided    ^^^Y  ^^  far  as  the  blastula.     Apparently 
(ffter'^Morgan)^^?    differentiation    is    slight    at    first,    and 
the  egg.  6  the  same    "ontog^env  assumcs  morc  and  more  the 

when  It  was  divided:  o       J 

iJSatld  as^at  l^^d     character  of  a  mosaic  work  as  it  goes 

two  half  embryos  in      fr-i-r-in^o-rr!   " 
the  i6-cell  stage;  e,      -Or^\a^a. 

pktf'b?aSuirs°'/^        Some    aberrancies    of    regeneration.— 

the  gaSmil^^Tage"    Ordinarily   after   mutilation,    if  normal 
no?maUizr°^^^^^    couditions  bc  maintained,   regeneration 

tends  toward  the  production  of  parts 
like  those  removed.  When  the  head  is  cut  off  a  hydra  it 
produces  a  new   head,    and   not   a   foot.     What    marked 


THE   LIFE  CYCLE 


3:9 


antero  posterior  polarity,  for  example,  is  shown  by  the  in- 
cised planarian  of  figure  205 /z,  which  is  producingnew heads 
where  the  strips  of  severed  tissue  are  directed  forward,  and 
tails  where  these  are  directed  backward.  But  the  expected 
does  not  always  happen  in  regeneration.  In  at  least  one 
genus  of  earthworms,  if  any  number  from  one  to  five  of 
the  front  segments  of  the  body  be  cut  off,  these  will  be 
replaced  in  like  number;  but  if  a  dozen  or  twenty  or  any 
number  of  segments  more  than  five  be  cut  away  from  the 
front  end,  only  five  will  be  regenerated  in  their  stead;  and 
if  more  than  the  anterior  half  of  the  body  be  cut  away, 
from  the  front  end  of  the  posterior  piece  there  wdll  develop 
not  a  new  head  but  a  new  tail.  Apparently,  there  is  a  limit 
to  anterior  polarity. 

The  hydroid  Antennaria  regenerates  a  new  head  when  the 
decapitated  stem  is  kept  in  the  upright  position,  but  a  new 
foot  when  it  is  kept  in  inverted  position.  And  stems  of  the 
hydroid  Pennaria,  which  regenerate  heads  under  ordinary 
circumstances,  w411  regenerate  roots  if  the  cut  ends  are  held 

^-  against  a  solid  support.     From 

the  severed  eye-stalkof  a  craw- 
fish (or  almost  any  other  deca- 
pod crustacean)  a  new  eye 
never  develops,  but  on  the 
contrary,  if  there  be  any  re- 
generation (as  there  is  pretty 
sure  to  be  if  the  animal  be 
young,  and  the  conditions 
favorable  for  growth),  it  is 
usually  a  jointed  appendage, 
more  or  less  antenna-like,  and 
at  its  best  development  dis- 
tinctly bi-ramous,  that  grows 
out  in  the  eye's  stead  (fig.  209). 


Fig.  209.  Regeneration  of  the 
stalked  eye  of  the  crawfish  (after 
Miss  Steele).  Inq  a  simple  appen- 
dage is  regenerated  in  the  place 
of  the  eye;  r,  a  biramous  appen- 
dage, that  regenerated  in  the 
place  of  the  eye  of  another  speci- 
men. 


360  GENERAL  BIOLOGY 

Study  45.    Experiments  with  regeneration  in  planarians. 

Materials  needed:  Plenty  of  living  planarians,  in  indi- 
vidual dishes  of  clean  water.  This  is  a  running  experiment, 
requiring  repeated  observations  at  successive  laboratory 
periods.  " 

Cut  small  pieces  from  some  of  them,  cut  others  in  two  in 
the  middle,  at  various  planes,  and  make  diagonal  clefts  in 
others  to  observe  polarity  of  the  partly  severed  pieces. 

Divide  the  bodies  of  a  number  of  the  animals.  They 
may  be  cut  with  fine  and  sharp  scissors  while  creeping,  fully 
extended,  on  a  piece  of  thin  wet  paper;  cut  paper  and 
planarian  together,  at  single  rapid  but  careful  strokes. 
Excessive  cutting  up  of  the  animals  may  be  avoided  by 
apportioning  the  work  among  several  members  of  the  class. 
(That  need  not  be  a  serious  consideration,  however,  since 
the  regenerated  pieces  may  be  returned  to  the  waters 
whence  the  whole  ones  were  originally  taken,  and  the  tribe 
will  have  been  increased  by  the  operation) . 

The  record  of  this  study  should  consist  of  sketches  of  the 
animal,  one  for  each  operation,  and  outline  drawings  of  the 
forms  assumed  at  subsequent  examinations. 

Grafting. — The  parts  of  two  organisms,  if  brought 
together  by  clean  cut  surfaces,  with  growing  parts  apposed, 
and  held  in  close  contact  for  a  time,  may  grow  together, 
and,  if  complemental  parts  be  taken,  they  will  thereafter 
function  as  a  single  organism.  This  is  grafting.  In  the 
higher  plants,  on  which  it  is  most  commonly  practiced,  the 
piece  that  is  to  represent  the  top  of  the  combined  plant 
is  called  the  cion,  the  rooting  piece  is  called  the  stock. 
These  two  parts  are  combined  into  one  in  a  number 
of  well  known  ways,  three  of  which  are  represented  in 
figure  210.  The  essential  things  in  the  practice  (with 
such  woody  plants  as  these  shown)  are  i)  the  bringing  of 


THE  LIFE   CYCLE 


361 


u 


\V 


the  cambium  or  growth  layer  of  scion  and  stock  into  close 
contact,  and  2)  protection  of  the  cut  surfaces  from  evapora- 
tion and  from  the  weather. 

Such  combinations  of  the 
higher  plants  are  possible  only 
between  rather  closely  related 
forms  (usually,  between 
members  of  the  same  genus), 
and  every  species  has  its  com- 
bination preferences,  which 
can  only  be  learned  by  trial. 
Pear  cions,  for  example,  will 
grow  well  on  quince  stocks,  but 
quince  cions  will  not  thrive  on 
the  pear.  Potato  and  tomato 
will  thrive  in  either  combina- 
tion, and  when  the  tomato  is 
the  cion,  both  potatoes  and 
tomatoes  may  be  produced  on  one  plant  (fig.  211). 

At  its  best  the  union  is  mainly  a  co-adjustment  of  trans- 
portation systems,  admitting  of  interchange  of  food  mater- 
rials;     each   part  retains  its    own    in- 
dividuality,   and,    the    results    of   the 
combination    are    not    heritable.     The 
objects  of  grafting  are  mainly  two; 

I.  To  combine  the  characters  of 
two  species  in  one  individual. 
Thus,  in  order,  to  add  to  the  good 
qualities  of  certain  apples  the 
hardiness  of  the  Siberian  crab,  apple 
cions  are  grown  on  crab  stock.  In  order 
to  adapt  certain  plums  to  southern 
soils,  plum  cions  are  grown  on  peach  ^\°he  pUntp^iXS  by 
stock.     When  the  vineyards  of  France       frfpStoTock!  '''°° 


Fig.  210.  Grafting  methods  [with 
plants,  a,  splice  grafting;  b,  cleft 
grafting;  c,  bud  grafting  (or  more 
commonly  called  budding).  u,u,u, 
u,  u,  cions.  V,  V,  v,  v,  stocks. 
The  second  figure  of  the  cleft  graft 
shows  how  the  grafting  wax  is 
applied  to  cover  the  wound. 


362 


GENERAL  BIOLOGY 


were  being  destroyed  by  the  imported  American  grape 
phylloxera  (a  root  infesting  aphid,  Phylloxera  vastatrix), 
the  situation  was  saved  largely  by  grafting  wine  grape 
cions  on  stocks  of  the  hardier  and  immune  American 
grapes. 

2.  To  perpetuate  in  the  fruiting  part  of  the  combination 
a  valuable  variety;  one  that  does  not  breed  at  all,  (as  for 
example,  a  seedless  grape  or  orange)  or  one  that  does  not 
breed  true.  In  such  case  the  kind  of  stock  used  is  of  little 
consequence,  except  as  it  is  a  good  feeder  for  the  cion. 

Grafting  in  animals. — Such  combinations  of  parts  are  not 
so  readily  made  in  animals.  The  specialized  contractility 
of  the  animal  body  is  against  it.  It  is  harder  to  keep  the 
growing  parts  in  close  apposition,  while  being  knit  together. 
Advantage  may  be  taken  of  quiescent  periods  in  the  life  of 
the  individual  when  stored  food  is  available  for  growth,  such 
as  the  early  embryonic  stages  of  frogs  (fig.  212)  and  the  pupal 

stages  of  insects,  etc.  Thus 
moth  pupae  of  the  right  age 
carefully  cut  in  two  across 
the  base  of  the  abdomen,  and 
carefully  handled  to  prevent 
loss  of  blood  have  been  united 
successfully  in  cross-combi- 
nations, the  parts  being 
sealed  with  paraffine  while 
being  knit  together.  An- 
tennae, and  wings  have  been 
cross-grafted  in  similar  man- 
ner. By  uniting  male  bodies 
with  female  abdomens,  fe- 
males having  the  appearance  of  males  have  been  produced. 
Similarly,  male  and  female  wings  and  antennae  have 
been  combined  upon    the    two    sides    of    one  individual. 


Fig.  212.  Diagram  of  grafting 
operation  on  frog  larvae  (after 
Harrison),  a,  the  larva  at  suit- 
able age  for  grafting;  b,  the 
same  larva,  older,  to  which  has 
grafted  the  tail  of  a  larva  of 
another  species. 


THE  LIFE  CYCLE  363 

Objects. — The  purpose  of  regeneration  and  grafting  experi- 
ments on  animals  has  been  to  obtain  new  side  Hghts  on  the 
nature  of  the  organism.  Nature  furnished  the  hints  for 
the  first  experiments  tried.  The  rooting  of  detached 
twigs  of  the  crack  wiUow  might  have  suggested  to  anyone  the 
possible  rooting  of  cuttings.  The  finding  of  regenerating  star- 
fishes, broken  in  the  surf,  might  have  suggested  regeneration 
experiments  on  animals,  and  if  a  portion  of  an  animal's 
body  from  which  the  sex  organs  were  removed,  were  able, 
as  it  is  in  fact  in  some  cases,  to  reproduce  the  missing  parts 
with  sex  organs  included,  then  the  experiment  w^ould  seem  to 
have  shown  that  the  distinction  between  body  plasm  and 
germ  plasm  is  not  to  be  too  sharply  drawn.  Although  the 
sex  cells  would  normally  come  from  the  sex  organs  removed, 
they  might  come  from  new  sources  in  the  body. 

Study  44.     Grafting  practice  with  plants. 

Materials  needed:  Selected  and  over- wintered  cions  and 
rooted  seedlings  or  other  stocks  for  their  reception;  grafting 
wax  (see  appendix)  and  sharp  pocket  knives. 

It  will  be  worth  the  time  of  a  laboratory  period  for  the 
student  to  make  with  his  owm  hands  the  combination  of 
parts  of  two  species,  and  later  to  see  them  growing  as  one. 
Different  types  of  grafting  may  be  demonstrated  also,  and 
the  later  matured  results  of  previous  operations.  The  work 
should  be  directed  by  someone  who  has  had  practical 
experience. 

The  record  of  the  study,  should  be  an  illustrated  account 
of  the  student's  own  operations  and  observations. 

Reserve  potentialities  of  the  living  substance. — The  studies 
of  this  chapter  should  have  been  convincing  of  the  wide 
range  of  methods  by  which  the  ends  of  life — the  preserva- 
tion of  races — are  accomplished.  We  began  this  chapter 
by  speaking  of  the  normal  course  of  life,  which  is  merely  the 


304  GENERAL  BIOLOGY 

more  usual  course  and  the  more  primitive.  All  the  devia- 
tions from  this  course  that  we  have  been  studying,  have 
become  thoroughly  normalized  in  the  races  that  exhibit 
them;  the  methods  of  development  are  stereotyped  alike 
for  all.  Whatever  the  course  of  life,  each  individual  of  a 
species  follows  it  with  the  most  minute  exactness.  And 
yet,  when  something  happens  to  block  the  usual  course, 
another  may  be  followed,  as  regeneration  and  grafting 
experiments  most  plainly  show,  to  reach  the  same  end. 
There  are  reserves  of  power  for  development  that  the  ordinary 
circumstances  of  life  do  not  draw  upon ;  accidents  and  losses 
reveal  their  existence.  If  a  member  be  maimed  and  a  por- 
tion of  its  tissues  be  injured  beyond  repair,  the  injured  part 
must  be  removed  and  new  tissue  fashioned  in  its  stead. 
Phagocytes  enter  a  wound  to  clear  away  old  materials,  and 
the  blood  brings  new  materials  to  be  gradually  fashioned 
into  the  form  of  the  old.  This  is  artificial  regeneration; 
but  nature  makes  use  of  these  same  pathologic  methods  in 
the  removal  of  old  tissues  and  the  building  of  new  in  meta- 
morphosis. 

That  the  functional  activity  of  certain  parts  of  organisms 
may  be  increased  by  selection  is  shown  by  the  increased  milk 
production  of  the  best  dairy  breeds  of  cattle,  and  by  the 
increased  egg  production  of  fowls,  etc.  Selection  has  made 
the  dairy  cow  an  improved  machine  for  turning  hay 
and  ensilage  into  milk.  But  nature  presents  examples  of 
the  exaggerated  activity  of  special  functions  yet  more 
striking.  One  such  has  been  fittingly  described  by  Lloyd 
Morgan  in  the  following  words: 

"There  is  perhaps,  no  more  wonderful  instance  of  rapid 
and  vigorous  growth  than  the  formation  of  antlers  of  deer. 
These  splendid  weapons  and  adornments  are  shed  and 
renewed  every  year.  In  the  spring  when  they  are  growing, 
they  are  covered  by  a  dark  skin,  provided  with  short,  fine, 


THE   LIFE   CYCLE  365 

close-set  hair,  and  technically  termed  'the  velvet.'  If  you 
lay  your  hand  on  a  growing  antler,  you  will  feel  that  it  is  hot 
with  the  nutrient  blood  that  is  coursing  beneath  it.  It  is, 
too,  exceedingly  sensitive  and  tender.  An  army  of  tens  of 
thousands  of  busy  living  cells  is  at  work  beneath  that  velvet 
surface,  building  the  bony  antlers,  preparing  for  the  battles 
of  autumn.  Each  minute  cell  knows  its  work,  and  does  it 
for  the  general  good,  so  perfectly  is  the  body  knit  into  an 
organic  whole.  It  takes  up  from  the  nutrient  blood  the 
special  materials  it  requires;  out  of  them  it  elaborates  the 
crude  bone-stuff,  at  first  soft  as  wax,  but  ere  long  to  be  as 
hard  as  stone;  and  then,  having  done  its  work,  having 
added  its  special  morsel  to  the  fabric  of  the  antler,  it  remains 
embedded  and  immured,  buried  beneath  the  bone  products 
of  its  successors  or  descendants.  No  hive  of  bees  is  busier, 
or  more  replete  with  active  life  than  the  antler  of  a  stag  as  it 
grows  beneath  the  soft,  warm  velvet.  And  thus  are  built  up 
in  the  course  of  a  few  weeks  those  splendid  'beams'  with 
their  'tynes'  and  'snags,'  which,  in  the  case  of  the  wapiti, 
even  in  the  confinement  of  our  Zoological  Gardens,  may 
reach  a  weight  of  thirty-two  pounds,  and  which  in  the  free- 
dom of  the  Rocky  Mountains,  may  reach  such  a  size  that  a 
man  may  walk  without  stooping,  beneath  the  archway  made 
by  setting  up  upon  their  points  the  shed  antlers.  When  the 
antler  has  reached  its  full  size,  a  circular  ridge  makes  its 
appearance  a  short  distance  from  the  base.  This  is  the 
'burr' which  divides  the  antler  into  a  short  'pedicel'  next 
the  skull,  and  the  'beam'  with  its  branches  above.  The 
circulation  in  the  blood  vessels  of  the  beam  now  begins  to 
languish,  and  the  velvet  dies  and  peels  off,  leaving  the  hard, 
dead  bony  substance  exposed.  Then  is  the  time  for 
fighting,  when  the  stags  challenge  each  other  to  single 
combat,  while  the  hinds  stand  timidly  by.  But  when 
the  period  of  battle  is  over,  and  the  wars  and  loves  of  the 


366 


GEXERAL    BIOLOGY 


year  are  past,  the  bone  beneath  the  burr  begins  to  be  eaten 
away  and  absorbed,  through  the  activity  of  certain  large 
bone-eating  cells,  and,  the  base  of  attachment  being  thus 
weakened,  the  beautiful  antlers  are  shed;  the  scarred  sur- 
face skins  over  and  heals,  and  only  the  hair-covered  pedicel 
of  the  antlers  is  left/' 

Antler  development  on  the  part  of  the  male  is  no  less 

remarkable,  al- 
though far  less  im- 
portant, than  the 
nrgSimc  response 
on  the  part  of  the 
female  that  follows 
upon  fertilization 
r/f  the  egg  and  re- 
sults in  the  produc- 
tion and  nurture  of 
the  young.  Figure 
2  13  is  intended  to 
show  how  quick  is 
this  response  to 
fertilization  in  the 
common  spreading 
d  ogbane  .  If  a 
flower  fail  of  fertil- 
ization it  dies,  but 
if  fertilized,  the  fruit  which  then  develops  from  it  may 
reach  full  size  before  the  last  of  the  flowers  on  the  same 
peduncle  have  faded. 

These  examples  of  organic  activity,  suddenly  and  inter- 
mittently recurring,  are  the  results  of  internal  (perhaps 
orthogenetic)  tendencies.  But  the  reserves  of  develop- 
mental power  which  organisms  possess  may  be  tapped  by 
outside  agencies  as  well.     Gall  insects  for  example,  have 


Fig.  213.  New  seed  pods  of  the  spreading  dog- 
bane (Apocynum),  showing  quick  response  to 
fertiUzation. 


THE   LIFE  CYCLE 


367 


turned  to  profit  their  ability  to  call  forth  plant  growths  in 
excess  of  the  normal.  We  have  already  noted  how  often 
galls  are  fruit -like  in  form  (fig.  214).  The  cone  gall  of  the 
willow  (fig.  203)  is  not  a  deformed  shoot,  but  an  overgrowth 
(hypertrophy)  of  tissue  superadded  to  the  normal  growth 
of  the  shoot. 

Organic  harmony. — Whether  an  organism  develop  out  of 
an  egg  under  normal  or  under  artificially  altered  circum- 
stances, whether  out  of  a  piece  of  a  pre-existing  organisms  or 
out  of  pieces  of  two  put  together,  if  it  develop  at  all  it  is 
pretty  sure  to- develop  with  organic  unity,  with  symmetry 
and  proportion.  Its  dominant  tendency  is  toward  organic 
wholeness. 


Fig.   214.     A  pod-like  bud  gallon  Pistachia  (after  Kerner  and  Olivier)    show- 
ing response  to  external  stimulus. 


CHAPTER  VI. 

THE    ADJUSTMENT  OF  ORGANISMS  TO    ENVIRONMENT. 
"Life  is  response  to  the  order  of  nature." — Brooks. 

In  this  chapter  we  shall  attempt  a  more  careful  examina- 
tion of  the  phenomena  of  fitness,  selecting  arbitrarily  for 
the  purpose,  out  of  a  world-full  of  examples,  a  few  that  seem 
fairly  illustrative  and  typical. 

Plants  and  animals,  which  were  primitively  much  alike 
and  lived  under  more  or  less  uniform  conditions,  have  multi- 
plied, differentiated,  specialized,  and  spread  to  every  habit- 
able part  of  the  globe,  and  have  become  adapted  to  condi- 
tions of  utmost  diversity  and  complexity.  Fitness  to  meet 
these  conditions  is  a  necessity  of  existence  under  them. 
Unfitness  so  pronounced  as  not  to  adm.it  of  getting  a  living 
or  of  leaving  descendants,  would  mean  for  any  species  speedy 
elimination.  That  all  living  things  are  adjusted  to  their 
places  in  the  world  is  most  obvious;  how  this  has  come 
about  is  a  subject  of  much  speculation  at  the  present  day. 
We  may  not  be  able  to  determine  whether  the  initiative  of 
the  variable  organism  or  the  impress  of  environing  condi- 
tions has  been  the  major  factor  in  producing  the  results,  but 
we  can  at  least  see  the  sort  of  facts  on  which  all  the  theories 
advanced  in  their  explanation  are  based.  As  a  matter  of 
convenience  we  will  divide  our  studies  of  this  subject  into 
three  groups,  according  to  the  more  prominent  phenomena 
involved,  as  follows: 

Adjustment  in  place  and  time. 
Adjustment  in  manner  of  life. 
Adjustment  in  bodily  characteristics. 


ADJUSTMENT  OF  ORGAMSMS  TO  ENVIRONMENT     369 

I.     ADJUSTMENT    IN     PLACE     AND    TIME. 

We  go  to  the  woods  for  squirrels,  to  the  marsh  for  snipe 
and  to  the  lake  for  fish.  We  do  not  expect  to  find  either  in 
the  place  of  the  other;  indeed,  we  know  they  could  not  live 
if  they  exchanged  places.  If  we  likewise  go  to  the  beach 
for  sand  or  to  the  mine  for  gold,  we  know  that  either  might 
exist  as  well  unchanged  if  put  in  the  place  of  the  other.  The 
gold  or  the  sand  may  have  lain  unchanged  for  ages,  but 
squirrel  and  snipe  and  fish  have  developed  with  their 
environment,  and  are  developing  still. 

It  is  not  everywhere  in  the  woods  that  we  find  squirrels. 
They  have  their  own  particular  haunts.  They  like  the  nut- 
bearing  trees,  and  shun  the  thorny  locusts.  They  like  cer- 
tain bird  neighbors  and  dislike  others.  In  the  water  we 
find  pickerel  and  top-minnows  feeding  at  the  surface,  cat- 
fishes  and  mud-minnows  feeding  on  the  bottom,  and  other 
fishes  foraging  between;  different  forms  of  life  at  different 
levels;  and  likewise,  passing  out  from  deep  water  shoreward 
we  find  that  every  change  of  forage  and  shelter  brings  with 
it  its  own  peculiar  forms  of  life.  The  more  closely  we  look 
into  any  environment  the  more  we  see  of  small  and  seques- 
tered species,  restricted  in  range  and  peculiar  in  mode  of 
life,  segregated  into  definite  and  sharply  delimited  haunts. 
The  physical  conditions  of  life  in  the  water  are  still  simple, 
but  with  the  multiplication  of  individuals  and  differentia- 
tion of  species,  by  reason  of  the  stress  of  competition  on 
every  hand,  the  biological  conditions  have  become  severe. 
Only  a  few  of  the  stronger  and  larger  species  frequent  the 
open  water,  and  these  only  when  they  have  attained 
maturity;  the  great  majority  of  the  lake's  inhabitants  dwell 
in  some  restricted  sphere.  The  great  sturgeon  may  roam 
the  lake  at  will,  but  the  little  darters,  and  infant  sturgeons 
as  well,  must  keep  to  shelter. 


370 


GENERAL  BIOLOGY 


I.     Local  distribution  of  green  plants. 

The  distribution  of  plants  over  the  larger  regions  of  the 
earth  is  determined  chiefly  by  physical  and  climatic  condi- 
tions. We  can  see  the  effect  of  temperature  by  passing 
from  the  stunted  and  scanty  vegetation  of  polar  regions  to 


Fig.  215.     Engelmann's  Spruce  from    a  sheltered   valley  (altitude 
7600  ft.)-      Photo  by  D.  M.  Andrews. 

the  luxuriant  forests  of  the  tropics;  of  winds  (figs.  215 
and  216)  and  altitude  and  drouth,  by  crossing  mountain 
and  desert.  AVe  can  see  the  effect  of  water  and  sunshine  by 
crossing  a  narrow  ravine,  from  its  moist  and  shaded  north 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     371 

slope  to  Its  dry  and  sunny  south  exposure;  or  we  can  see 
it  by  walking  from  the  north  side  of  our    house  around  to 


• 

■■•"■"  '■'■  ■■■^-'--    ■;■  ■■  "¥'" 

- 

^*^ 

' 

^^ 

^^m   ' 

* 

m 

> 

b 

^^^^P 

^^ 

^^^ 

■^',S-^< 


■:i*f  .«f1 


Fig.   216.      Engelmann's  spruce   from   an  exposed  mountain  side 
(altitude  lo.Soo  ft.).      Photo  by  D.  M.  Andrews. 


the  south  side.  Food  and  water  are  the  primary  requis- 
ites of  plants ;  but  green  plant  food  is  nearly  everywhere 
present — the  carbon  in  the  air,  and  the  other  food  materi- 
als in  the  soil ;  but  water  is  not  so  uniformly  distributed 
over  the  surface  of  the  earth.     So  it  has  come  about  that 


372  GEXERAL  BIOLOGY 

the    distribution    of    water    has    largely    determined  the 
grouping  of  terrestrial  plants  into  natural  societies: 

Hydrophytes — Plants  accustomed  to  abundant  avail- 
able moisture. 

Mesophytes — Plants  that  live  under  intermediate  condi- 
tions. 

Xerophytes — Plants  that  live  where  the  water  supply- 
is  scanty,  and  that  have  deep  roots,  and  many  adaptations 
for  conserving  the  water  supply. 

AVithin  each  of  these  groups  the  distribution  of  the  mem- 
bers in  relation  to  each  other — their  mutual  adjustment  in 
place — is  determined  more  largely  by  exposure  to  light  than 
by  any  other  single  factor.  Besides  food,  green  plants  must 
have  light,  to  supply  the  energy  for  growth  that  their 
simple  foods  lack.  This  is  especially  true  of  the  mesophyte 
society,  with  its  extraordinary  diversity  of  size  and  form  and 
habitat.  Be  it  forest,  heath,  or  meadow,  we  always  find  it 
dominated  by  a  few  relatively  large  species  of  great  vegeta- 
tive vigor.  Around  and  between  these,  occupying  the 
interstices,  and  holding  what  soil  and  sunshine  they  can  get, 
are  a  host  of  lesser  species,  scattered,  diversified  and  often 
highly  specialized  as  to  their  mode  of  performing  particular 
functions.  It  is  among  these  that  we  find  the  most  special 
forms  of  plant-body  and  the  most  special  devices  for  secur- 
ing cross-pollination  and  seed  distribution,  etc.  A  few  of 
these  plants  of  the  undergrowth  sometimes  show  a  sort  of 
secondary  dominance, their  crowns  forming  imperfect  foliage 
strata  at  successively  lower  levels.  Thus  in  the  hard-wood 
forests  of  our  northern  mountains  there  is  often  a  top 
stratum  of  crowns  of  maple,  beech  and  birch  at  high  altitude ; 
a  secondary  stratum  of  the  spreading  tops  of  the  hobble- 
bush,  a  few  feet  above  the  ground,  and  a  third  stratum 
of  moss,  carpeting  the  floor  of  the  forest.  Often  in  oak 
woods  farther  south,  there  are  successively  lower  strata  of 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     373 

hazel  and  mandrake  and  moss,  and  in  the  soil  there  is 
likewise  a  more  or  less  definite  arrangement  of  the  roots  in 
strata,  less  easily  observed  because  hidden,  but  probably  as 
real,  because  supported  by  the  stratification  of  the  soil. 
The  smallest  herbs  usually  root  in  the  top  soil,  the  majority 
of  shrubs  in  the  subsoil,  while  many  of  the  trees  strike  root 
far  deeper.  By  these  means  the  resources  of  both  light  and 
soil  are  more  fully  utilized  and  a  more  abundant  and  varied 
flora  is  maintained. 

The  dominant  plants  are  usually  of  erect  habit  of  growth, 
conforming  more  or  less  closely  to  some  of  the  commoner 
typical  forms  shown  in  the  accompanying  diagram  (fig.  217); 


Fig.  217.     Diagrams  of    growth    habit   in     plants,     a,   rosette;   b,    scape;   c, 
wand;    d,  bush,  e;  crown;  /,  climbing;    g,  twining;    h,  trailing. 

but  growth  habit  varies  with  crowding  and  with  the  conse- 
quent restriction  of  the  light. 

Study  45.     Woodland  plant  society. 

Field  study. — Select  a  bit  of  woods  that  has  retained 
natural  conditions,  at  least  as  natural  as  possible.  Lay 
out  a  small  area,  a  strip  a  few  rods  long,  containing  some 
diversity  of  conditions,  for  a  detailed  study  of  its  green 
plant  population.  It  must  needs  be  a  small  area  in  order 
that  all  members  may  be  examined.  In  order  to  determine 
the  normal  characteristics  of  some  of  the  larger  or  rarer 
species  it  may  be  necessary  to  extend  observation  of  these 
over  a  wider  area. 


374  GENERAL   BIOLOGY 

Study  each  species  as  to  its  more  important  ecological 
characters  and  record  these  characters  briefly  in  a  table 
prepared  with  the  following  headings : 

Name. 

Duration   (annual,  biennial,  perennial). 

Increase  (aside  from  seeds,  by  offsets,  stolons,  tubers,  etc.) 

Social  habit  (solitary,  commingling,  copse  forming,  cover 
forming) . 

Growth  habit  (scape,  rosette,  wand,  bush,  crown.  If 
not  erect,  trailing,  twining,  climbing  or  epiphyte,  parasite, 
subterranean,    etc.) 

Rooting  in  (topsoil,  subsoil,  deep  soil,  rock  crevices,  rotten 
wood,  etc.) 

Favorite  situation. 

Favorite  exposure. 

Season  of  maximum  vegetative  activity  (spring,  early 
summer,  late  summer). 

Write  the  names  in  the  first  column  by  groups,  as 
follows : 

i    trees 
shrubs 
herbs 
Pteridophytes 
Bryophytes 
Thallophytes. 

The  record. — After  the  table  is  completed  (the  entire 
green  plant  population  of  the  area  selected  being  included 
therein),  then  wTite  out  briefly  your  interpretation  of  the 
facts,  as  to  the  relative  dominance  of  each  ecological 
characteristic,  and  possible  reasons  therefor. 

Adjustments  in  place  may  be  further  illustrated  by  the 
zonal  distribution  of  aquatic  seed-plants,  indicated  at  the 
right  in  figure  224.  This  represents  an  inviolable  order;  for 
the  shoreward  types  are  capable  of  shutting  out  the  light 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     375 

from  those  in  deep  water,  except  at  depths  they  themselves 
cannot  endure.  Adjustments  in  time  are  indicated  in  the 
last  column  of  the  preceding  table  for  the  single  season. 


Fig.  218.     A  damselfly  {Lesies  uncatus). 


These  are  mutual  adjustments  and  involve  succession  of 
periods  of  vegetative  activity.  Time  adjustments  that 
extend  over  long  periods,  and  that  accompany  slow  changes 


376 


GENERAL   BIOLOGY 


m. 


of  environment,  and  that  result  in  a  succession  of  floras, 
may  be  studied  if  there  be  available  a  series  of 
ponds  in  the  various  stages  of  filling,  or  if 
there  be  burned  over  tracts  or  fallow  fields  m 
the  various  stages  of  reforestation  Sugges- 
tions for  such  studies  may  be  found  in  a  num- 
ber of  modern  text  books  of  botany.  The 
adjustment  for  geologic  time  is  studied  in  the 
palaeontologic  reccrd,  and  is  the  history  of 
plant  life  on  the  earth  from  the  beginning. 


2.     Hibe?  nation  and  aestivation. 

Corresponding  to  the  seasonal  adjustments 
of  early  and  late  plants,  just  cited,  there  is 
seasonal  cessation  of  vital  activity  among 
animals.  In  our  temperate  climate,  many 
warm  blooded  mammals,  and  most  other 
resident  animals,  disappearon  the  advent  of 
cold  weather,  and  may  be  found  in  a  dormant 
condition,  in  winter  quarters.  They  are  hiber- 
nating. Their  temperature  is  barely  above 
freezing  point.  Their  metabolism  is  well 
nigh  at  a  stand  still.  In  the  spring  they  emerge 
in  good  condition  and  resume  their  wonted 
activities.  Nature  effects  great  economy  by 
limiting  their  foraging  operations  to  the  grow- 
ing season. 

On  the  other  hand,  in  the  hot  weather  of 
summer,  with  its  accompanying  drouth,  when 
there  is  not  enough  water  to  maintain  activity 
on  the  part  of  organisms  that  live  in  temporary 
shoals  there  results  another  resting  stage  that 
is  known  as  aestivation.  Thus,  through  the 
central  United  States  the  damselfly  shown  in 


rv- 


(, 


Fig.  219.  The 
sesti  V  at  i  n  g 
embryo  of 
L  e  s  t  e  s  .as 
seen  through 
the  translu- 
c  e  n  t  egg 
shell.  /,  la- 
b  r  u  m;  m, 
antenna;  n, 
mandible:  o, 
maxilla;  p, 
labium;  q,  r, 
s,  legs  of  one 
sid  i)"  t,  abdo- 
men. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT      37  7 

figure  2 18,  lays  its  eggs  in  the  stems  of  bur-reed  and  iris, 
growing  in  temporary  pools.  The  eggs  at  first  develop 
rapidly  as  in  other  damselflies,  and  reach  the  condition 
shown  in  figure  219  about  the  time  that  these    pools   nor- 


y 


Fig.  220.  Animals  that  withstand  dessication.  z  and  j,  a  tardigrade 
{Macrobiotus  hufelandi)  x,  extended,  creeping;  y,  in  a  state  of  apparent 
death,  dried;  z,  a.  votiiev  (Philodina  megalotrocha).  Internal  organs  ot  the 
tardigrade  shown  in  optic  section:  m,  pharynx;  n,  salivary  gland;  o, 
stomach;  p,  ovary;  i,  ii,  iii,  iv,  legs  of  one  side,  (z  and  y,  after  Hertwig, 
z,  after  Jennings. 

mally  "go  dry."  There  they  stop,  and  in  that  condition 
they  remain  until  the  rains  of  autumn  refill  the  pools, 
when  they  resume  development,  hatch  out  and  enter  the 
water. 

There  are  many  lesser  organisms,  notably  the  tardigrades 
and  rotifers  (fig.  220),  so  well  adjusted  to  the  exigencies  of 
drouth  they  can  get  along  and  maintain  themselves,  living 


378  GENERAL  BIOLOGY 

in  rain  water  spouts,  and  in  stone  urns,  that  are  alternately 
drenched  with  showers  and  baked  in  the  sun.  With  every 
sun-baking,  they  are  almost  completely  dessicated,  and 
become  contracted  and  wrinkled  into  almost  unrecogniz- 
able shapes;  but  with  the  next  shower  they  "soak  up"  again, 
and  resume  normal  activity. 

Study  46.     Observations  on    the   dessication  and  resuscita- 
tion of  rotifers. 

Materials  needed:  An  abundance  of  living  rotifers,  pref- 
erably of  the  genus  Philodina,  which  is  commonly  found  in 
the  dried  crust  of  the  bottom  in  stone  urns  in  cemeteries,  etc., 
and  which  may  be  cultivated  in  little  porcelain  dishes  w4th 
rain  water  in  the  laboratory.  For  convenience  of  handling, 
cultures  are  best  made  on  squares  of  fine-meshed  filter  paper 
laid  in  the  hollow  of  the  bottom  of  the  dishes.  For  methods 
of  handling,  of  concentrating,  of  isolating  the  rotifers  see 
appendix. 

The  student  should  obtain  specimens  at  one  laboratory 
period,  should  isolate  some  of  them  in  the  bottom  of  a  hol- 
low ground  slide  in  the  hollow  of  a  piece  of  filter  paper  fitted 
thereto,  should  set  this  slide  away  uncovered  to  dry  by 
evaporation,  and  at  the  next  laboratory  period,  should 
examine  the  rotifers  dry,  and  then  should  cover  them  with 
water  and  watch  them  resuscitate. 

The  record  of  this  study  should  consist  of  notes  on  and 
sketches  of  the  things  observed. 

J.     Local  distribution  of  animals. 

That  food  and  shelter  are  the  primary  factors  determining 
the  distribution  of  animals  is  almost  too  obvious  to  be 
stated.  Where  to  find  a  living  and  establish  a  home  is  the 
great  question  confronting  every  animal — even  man. 
Terrestrial  plants  live  where  they  must;   but  most  animals 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     379 


are  free  to  move  about  within  certain,  often  narrow,  limits, 
to  find  new  pasture  or  to  change  their  domicile.  In  a  small 
society  of  green  plants  it  is  comparatively  easy  to  find  all 
the  species,  for  they  are  fixed  in  place,  and  come  out  into 
the  light,  and  into  view;  but  so  different  is  the  case  with 
animals,  so  small  are  many  of  them  and  so  secretive  and 
elusive  of  habit,  that  there  is  not  an  acre  of  the  earth's  sur- 
face of  which  the  entire  animal  population  is  known.  Even 
of  that  class  of  large  animals  to  which  we  ourselves  belong, 
there  are  many  mammals  living  in  our  own  immediate 
environs  that  we  seldom  or  never  see. 

As  already  stated  in  the  opening  chapter,  herbivores  and 
carnivores,  parasites  and  scavengets  are  everywhere,  be- 
cause they  fulfill  permanent  functions  in  natural  society. 

The  herbivores  are, 
among  animals,  the  pro- 
ducing class;  all  the 
others  are  consumers. 
The  food  of  animals  is 
not  to  be  found  every- 
where, even  that  of  the 
most  omnivorous 
species.  The  deer  that 
roams  the  forest,  crop- 
ping the  leaves  and 
twigs  of  a  great  variety 
of  plants,  leaves  a  much 
greater  number  of  spe- 
cies untouched.  The 
caterpillars  of  the  gypsy 
moth  will  eat  the  leaves 
of    almost   every    green 

Fig.   221.     Photograph    from    life    of    a  tree,  but  mOSt    Catcrpill- 

young     and    active  Hag    weevil    larva  ^j-g    ^^^    g^^    ^f    ^    single 

{Mononychus  vulpeculus).  ** 


38o 


GENERAL     BIOLOGY 


genus  of  plants,  and  many  will  eat  only  of  a  single  species.  The 
result  of  the  competition  of  the  past  among  animals  seems 
to  have  been  toward  greater  localization  and  concentration 
of  food  supply — at  least  for  the  smaller  species.  The  flag 
weevil  (fig.  221)  eats  of  the  seeds  of  the  blue  flag  (Iris  versi- 
color) but  only  of  the  endosperm,  and  of  that  only  for  a 
few  weeks  when  it  is  newly  formed.  Likewise,  carni- 
vores, parasites  and  scavengers  all  have  their  peculiar 
tastes. 


> 


4 


■  ;^ 


v;y/// 


'I  i 


Fig.  222.     Diagram    illustrating     lines    of    ecological  specialization     among 
terrestrial  vertebrates. 

That  these  tastes  may  best  be  gratified  under  those  condi- 
tions that  at  the  same  time  furnish  the  best  shelter  and 
domicile  for  each  species  is  a  truly  wonderful  and  altogether 
admirable  feature  of  their  adjustment. 

Primitive  terrestrial  animals,  recently  come  up  from  the 
water,  were  doubtless  "creeping  things,"  with  feet  adapted 
more  for  propulsion  than  for  the  support  of  the  body 
(fig.  no,  page  180).  In  time  their  descendants  were  able  to 
get  up  on  their  feet  and  walk.     With  better  powers  of  loco- 


ADJUSTMENT  OP  ORGANISMS  TO  ENVIRONMENT     381 

motion  they  were  better  able  to  possess  the  land,  and  they 
multiplied  in  numbers  and  competition  ensued.  Super- 
added to  the  stress  of  competition  was  the  direct  onslaught 
of  active  enemies.  Conditions  became  hard,  and  various 
shifts  for  a  living  were  resorted  to.  The  main  lines  these 
shifts  could  take  were  determined,  however,  by  environ- 
ing conditions.  There  was  room  to  run  in,  if  speed  could 
be  attained.  There  was  soil  to  hide  in,  if  one  could  dig; 
there  were  trees  to  climb ;  there  was  w^ater  to  dive  in ; 
and  if  anything  could  fly  the  air  offered  the  best  of  all 
ways  of  escape. 

So  land  animals  differentiated,  somewhat  as  indicated 
graphically  in  the  accompanying  diagram  (fig.  222)  into 
cursorial,  fossorial,    arboreal,   aquatic  and   aerial    groups. 

Size. — Owing  to  the  nature  of  the  environment,  its 
limited  quantities  of  food,  its  limited  and  irregularly 
distributed  accommodations  for  shelter,  size  came  early  to 
be  a  determining  factor  in  the  adjustment.  For  the  small 
animal,  while  at  a  disadvantage  in  point  of  strength,  is  at  a 
great  advantage  when  it  comes  to  finding  food  and  shelter. 
A  flag  weevil  can  find  a  life's  provision  in  one  chamber  of  an 
iris  seed  capsule,  and  leave  enough  seed  untouched  to  main- 
tain the  plant  stock,  while  an  ox  may  browse  to  the  point  of 
extermination  all  the  herbage  on  half  an  acre  of  ground. 

The  kind  of  differentiation  of  habitat  possible  to  the  larger 
vertebrates,  w^as  possible  to  terrestrial  invertebrates  upon  a 
smaller  scale.  The  runners,  climbers,  burrowers,  etc., 
among  the  beasts  of  the  forest  have  their  counterparts  in 
groups  of  like  habits  among  the  insects  of  the  meadow. 
Moreover,  among  the  lesser  animals  that  climbed  the  tree  or 
that  went  down  into  the  burrow  of  the  beast,  there  was  a 
secondary,  parallel  differentiation;  so  that  on  the  trunk  of 
the  tree,  and  on  the  walls  of  the  burrow  we  find  small  bur- 
rowing,    running,    jumping    and    flying    forms       Indeed, 


382 


GENERAL  BIOLOGY 


even  on  the  back  of  the  ox  there  are  parallel  phenom- 
ena of  distribution ;  there  are  fly  larvae  that  burrow  beneath 
the  skin,  there  are  ticks  that  cling  to  the  surface,  fleas  that 
run  and  jump  about,  and  flies  that  take  wing. 

Thus,  the  body  of  the  large  plant  or  animal  becomes  a  unit 
of  environment  for  a  host  of  dependent  forms.  Miniature 
units  are  found  in  single  organic  products,  such  as  the  ear  of 


Fig.  223.      Young  woodchuck  {Arctomys    monax)  in  the  mouth  of  his  burrow. 
Photo  by  T.  L.  Hankinson. 

com,  the  head  of  cabbage,  or  any  of  the  larger  fleshy  fruits; 
how  many  inhabitants  there  are  dwelling  in  each  of  these, 
and  how  well  they  are  localized  and  adjusted  in  place  and 
time,  may  be  learned  from  the  reports  of  our  agricultural 
experiment  stations.  The  cone  gall  of  the  willow  has  a  con- 
siderable population,  distributed  in  place  as  indicated  in 
figure  36,  (page  46).     In  cases  like  these  the  distribution  is 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     383 


different  from  that  on  plane  surfaces,  as  indicated  above; 
but  it  is  always  conditioned  by  and  always  conforms  to  the 
nature  of  the  environment. 

It  is  the  terrestrial  vertebrates  that  we  know  best  among 
animals  so  we  will  next  attempt  a  cooperative  statistical 
compilation  of  facts  bearing  directly  on  the  mutual  adjust- 
ments of  these. 

Study  47.      The  local  resident    terrestrial    vertebrate  fauna: 
its  ecological  distribution;  a  compilation- study. 

Prepare  a  table,  leaving  a  column  at  the  left  hand  for 
group  names,  with  the  following  column  headings,  abbre- 
viated as  desired: 
Name. 

Inhabits  (forest,     heath,     meadow,    marsh,    shores, 

desert  place :  indicate   special    habitats  in 
any  of  these) . 


Eats  what 


(  Plants 
(  Animals 


(specify   the   kind 
of  food  eaten.) 


Forages 


I  w^here 

)  when,  (day,  night,  etc.) 
Special  means  or  apparatus  for  getting  food, 
j  where 
(  when  (dates) 
Constructs  or  takes  advantage  of,  what  special  shelter. 

What  sort  of  activities  (running, 
jumping,  dodging,  burrowing, 
flying,  diving,  etc.) 
What  sort  of  organic  defense  (bad 
odor,  bad  flavor,  defensive 
armor,  protective  coloration, 
etc.) 


Escapes  enemies  by   < 


384  GENERAL  BIOLOGY 

Arrange  the  names  by  groups  at  the  left  hand,  mam- 
mals, birds,  reptiles  and  amphibians. 

Fill  out  the  table  as  far  as  possible  from  personal  knowl- 
edge and  observation.  For  the  balance  consult  reference 
literature,  or  any  other  source  of  reliable  information.  In  a 
class  of  students  this  may  be  facilitated  by  division  of 
labor.  If  blanks  still  remain  they  should  be  useful  as 
indicating  gaps  in  the  knowledge  of  the  local  species. 

Such  a  table  as  the  foregoing  kept  by  the  laboratory  and 
added  to,  year  by  year,  by  succeeding  classes  as  knowledge 
of  the  fauna  increases,  may  grow  into  a  most  useful  and  reli- 
able ready-reference  chart. 

The  record. — Complete  the  table  so  far  as  possible  and 
then  write  out  briefly  your  own  interpretation  of  the  facts 
contained  in  it.  These  facts  should  give  rise  to  many  legiti- 
mate questions.  Is  there  any  clear  relation  between  any 
systematic  group  and  any  particular  habit  of  feeding?  of 
locomotion  ?  What  kind  of  habitat  has  the  largest  number 
of  species  in  its  population  and  why?  What  habits  are 
shown  by  the  smallest  number  of  species  and  why  ?  Is  there 
any  clear  relation  between  size  of  the  animals  and  habitat? 
Between  size  and  feeding  habits?  Between  size  and  habits 
of  locomotion?  etc.,  etc. 

Animal  migrations  are  sudden  shifts  of  place  that  de- 
mand good  powers  of  locomotion.  When  of  irregular  oc- 
currence, as  is  usually  the  case  with  the  migration  of 
mammals  like  the  lemmings,  and  of  insects  like  the  Rocky 
Mountain  locust,  they  necessitate  biological  readjustment 
in  both  the  localities  between  which  the  migration  occurs; 
for  the  natural  balance  is  disturbed  in  both  places:  but 
when  well  established  as  a  normal  part  of  a  mode  of  life, 
as  in  the  regular  annual  migrations  of  birds  between  their 
summer  and  winter  homes,  the  adjustment  becomes  per- 
fected, not  only  as  adjustment  in  place  and  time,  but  also 
as  adjustment  between  different  places  and  seasons. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     385 

4.     Pond  life. 

The  pond  is  a  well  defined  unit  of  environment.  Aquatic 
forms  of  life  are  hemmed  in  by  its  shores.  They  are  easy  to 
find,  easy  to  collect  and  easy  to  keep  alive  and  to  observe. 
As  it  is  not  difficult  to  determine  the  place  of  each  in  the 
pond,  the  following  study  should  offer  opportunities  fo*- 
greater  definiteness  in  field  observations. 

The  animals  of  the  pond  are  in  part  forms  that  have 
always  been  aquatic,  and  in  part  land  forms  returned  to  the 
water.  Among  the  latter,  some  have  retained  their  terres- 
trial mode  of  breathing;    some  have  become  readapted  to 


Fig.  224.  Diagram  of  distribution  of  pond  life.  The  right  side  illustrates 
the  zonal  distribution  of  the  higher  plants.  /,  shore  zone;  2,  standing'emerg- 
ent  aquatics;  J,  aquatics  with  floating  leaves;  4,  submerged  aquatics;  j, 
floating  aquatics;   6,  free  swimming  algae  of  the  open  water. 

The  left  side  represents  the  principal  features  of  the  distribution  of  animals, 
r,  5,  t,  u,  are  the  air-breathers;  v,  w,  x,  y,  and  z,  are  the  water-breathers,  as 
per  accompanying  table. 

the  water,  and  have  respiratory  apparatus  of  a  strictly 
aquatic  type.  The  problem  of  getting  air  has  been  a 
primary  one  determining  their  distribution. 

Collectively  the  animal  life  of  the  pond  may  be  divided 
into  two  groups  according  to  whether  the  air  is  taken  free  or 
dissolved  in  the  water;  easily  recognizable  ecological  sub- 
divisions will  then  be  those  of  the  following  table.  Their 
places  are  indicated  graphically  in  the  accompanying 
diagram  (fig.  224). 


386 


GENERAL  BIOLOGY 


Forms  breathing 
free  air 


Forms  breathing 
air  dissolved 
in  water 


1.  Forms  running  on  the  surface 
(water  skaters,  etc.) 

2.  Forms  lying  on  the  surface 
(whirligig  beetles,  etc.) 

3.  Forms  hanging  at  the  surface, 
tipping  the  surface  film  (diving 
beetles,  etc.) 

4.  Forms  far  below  the  surface,  con- 
necting therewith  by  means  of  a 
long  respiratory  tube.  (Ranatra, 
rat-tailed  maggot). 

5.  Free  swimming  forms,  (corethra, 
etc.) 

6.  Climbing  and  clinging  forms, 
(mayfly,  nymphs,  etc.) 

7.  Attached  forms,  (hydras,  bryo- 
zoans,  etc.) 

8.  Forms  that  walk  or  lie  upon  the 
bottom,  (crawfish,  etc.) 

9.  Forms  that  burrow  in  the  bottom, 
(Ephemera,  etc.) 

Study  48.     A  laboratory  examination  of  typical  pond  animals. 

Materials  needed:  Plenty  of  living  specimens  of  the 
several  types  of  pond  animals  mentioned  in  the  foregoing 
table ;  individual  beakers  of  water  in  which  to  examine  them. 

First  compare  together  representatives  of  the  two  main 
groups;  a  whirligig  (Gyrinus  or  Dineutes) ,  representing  the 
groups  that  breathe  free  air,  and  a  Mayfly  or  damselfly 
nymph  (fig.  225)  representing  the  groups  that  breathe 
the  dissolved  air.  Put  both  in  a  large  beaker  of  water  and 
watch  them ;  observe  that  the  beetle  carries  a  bubble  of  air 
at  its  wing-tips  as  it  swims;  its  respiratory  apertures  are 
beneath  its  wings.     Observe  the  cleavage  of  the  water  when 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     387 

it  rises  to  the  surface;  note  the  water  repellent  surface; 
compare  with  the  surface  of  the  nymph.  Compare  the  two  as 
to  what  happens  when  they  stop  swimming;  which  one 
rises  to  the  surface  like  a  cork?  Compare  with  one  of  the 
free-swimming  forms  in  respect  to  this.  Then  examine  the 
whirligig  more  carefully  i)  as  to  the  differentiation  of  its 
feet;  2)  the  extreme  specialization  of  its  hind  feet;  3)  the 
form  of  its  body  and  4)  the  differentiation  of  its  divided 
eyes,  into  an  upper  eye  to  look  into  the  air,  and  a  lower  one 
to  look  down  into  the  water;  all  are  express  adaptations  for 
living  on  the  surface.     Then  examine  the  other,  as  to  its 


Fig.   225.      The   nymph   of  a  damseltly    {Ischnuni  vcrticalis). 


climbing  feet,  the  gills  upon  its  abdomen  and  its  protective 
coloring. 

Then  compare  the  representatives  of  the  groups  i  to  4  as 
to  i)  position  in  the  water,  and  movements;  2)  mode,  if  they 
have  any  of  carrying  air;  3)  air  repellence  of  the  body  sur- 
face, and  4)  weight.  Air  carried  externally  can  be  recog- 
nized by  its  shine.  Push  a  skater  or  a  water-spider  (or  even 
a  housefly)  under  water  and  see  the  layer  of  air  enveloping 
its  whole  body. 


388  GENERAL  BIOLOGY       ' 

Then  compare  together  representatives  of  groups  5  to  9 
as  to  i)  diversity  of  form  and  habit;  2)  resting  position  in 
the  water.  Compare  together  dragonfly  nymphs  representing 
groups  8  (Libellula)  and  9  (Gomphus)  i)  as  to  form  of  body, 
2)  form  of  front  of  head,  and  3)  shape  and  position  of  feet. 

The  record  of  this  stud  7  may  consist  of  brief  comparative 
statements  of  the  things  personally  observed.  State  briefly 
the  characters  of  each  type  that  mark  its  fitness  for  the 
ecological  situation  to  which  it  belongs. 

Sttidy  4g.     A  field  study  of  the  pond  animals  in  their  native 

haunts. 

A  pond  should  be  selected  that  has  more  or  less  shore 
vegetation,  and  banks  dry  enough  to  admit  of  approach 
with  hand  nets.  A  small  pond  if  permanent  is  as  good  as  a 
large  one,  and  if  no  pond  be  available,  a  bay  off  a  lake  or 
river  will  offer  practically  the  same  forms. 

Apparatus  needed:  Individual  dip  nets,  beakers  and 
vials.     A  plankton  towing  net,  a  sieve  net  and  a  few  pails  or 

bowls  for  com- 
mon use  will 
also  be  advan- 
tageous. 

Let  the  collect- 
ing and  study 
be  individual. 

Collect  air 
breathers  at  the 
surface  with  a 
dip  net ;  such  as 
are  foraging  or 
hiding  down  be- 
low may  be  ob- 
tained later. 


Fig.  226.  Shells  of  fresh  ■water  snails,  a,  Planorbis; 
b^  Ancylus;  c,  Limnea;  d,  Physa.  (From  Morse's 
First  Book  of  Zoology,  a  pioneer  American  book  of 
nature-study). 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     389 

Sweep  the  open  water  with  the  dip  net  for  free  swimming 
forms.  (Most  of  these  are  obtained  more  readily  with  a 
plankton  net.) 

Sweep  the  submerc^ed  vegetation  with  the  dip  net  for  the 
climbing  and  clinging  forms ;  some  members  of  groups  2  and 
3  will  thus  at  the  same  time  be  obtained. 

Scrape  the  bottom  with  the  dip  net  for  bottom  forms; 
scrape  deeper  and  sift  out  at  the  surface, to  get  the  bur- 
rowers;  for  these  a  sieve  net  is  more  efficient. 

Take  up  submerged  sticks,  stones,  leaves,  etc.,  from  the 
water  and  examine  them  for  attached  forms  (the  examina- 
tion is  very  satisfactory  by  submersion  in  water  in  a  big 
white  bowl;  bryozoan  colonies  (see  fig.  i88a)  will,  however, 
be  easily  seen  without  this  submersion. 

Study  each  species  as  it  is  obtained ;  put  a  few  specimens 
into  a  beaker  of  clean  water  with  a  few  clean  pebbles  on  the 
bottom  and  some  stems  at  one  side  and  watch  it.  Determine 
to  which  of  the  nine  groups  it  belongs  and  write  its  ecologica 
characters  in  the  proper  place  in  a  table  prepared  with  the 
following  column  headings: 

Name. 

Stage  (larva,  pupa  or  adult,  etc.) 
Feeding  habits. 
Takes  air  how. 
Swimming  apparatus. 
Clinging  or  climbing  apparatus. 
Means  of  locomotion  other  than  swimming. 
Means  of  j      observation  of  enemies 

escaping  [      attack  of  enemies 

It  should  be  possible  to  obtain: 

Of  group  I,  water  skaters,  water  spiders,  springtails,etc. 
Of  group  2,  whirligig  beetles. 


390  GENERAL   BIOLOGY 

Of  group  3,  diving  beetles,  water  boatmen,  back  swim- 
mers, water  bugs,  mosquito  pupae,  cranefly  larvae, 
frogs,  snails,  etc. 

Of  group  4,  Ranatra  and  rat-tailed  maggot. 

Of  group  5,  Corethra,  mosquito  larvae,  Daphnia,  and  a 
number  of  other  micro-crustaceans. 

Of  group  6,  damselfly,  mayfly  and  some  dragonfly 
nymphs,  amphipods,  newly  hatched  amphibian 
larvae,  etc.) 

Of  group  7,  hydras,  vorticellidae,  bryozoans  (especially 
Plumatella),  etc. 

Of  group  8,  crawfishes,  dragonfly  nymphs,  Asellus,  etc. 

Of  group  9.  Tubifex,  dragonfly  nymphs,  small  mussels, 
nymphs  of  Ephemera,  etc. 

The  record. — Find  and  include  in  the  table  as  representa- 
tive an  assemblage  of  forms  as  possible.  Where  many  allied 
forms  of  closely  similar  habit  are  found,  use  but  one  example. 

II.       ADJUSTMENT    IN    MANNER    OF    LIFE, 

We  select  for  study  under  this  heading  three  subjects  only: 
i)  Symbiosis:     the  adjustment  in  mode  of  life  of  two 

different  organisms  enabling  them  to  live  together  in  union 

with  mutual  advantage. 

2)  Parasitism:  adjustment  in  mode  of  life  between  two 
different  organisms  for  the  benefit  of  the  smaller  and  for  the 
detriment  of  the  larger. 

3)  Pollen  production  in  flowering  plants  in  relation  to  its 
distribution;  the  adjustment  of  one  special  plant  function  in 
relation  to  physical  and  animal  environment. 

I .     Symbiosis 

Lichens  are  the  best  as  well  as  the  commonest  illustrations 
of  this  phenomenon.  Lichens  may  be  gathered  at  any  time 
from  the  trunks  of  trees,  from  stones  and  fences,  and  from 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     391 

many  other  dry  and  sterile  and  unpromising  situations. 
The  gray  encrusting  species  are  commonest,  but  many  forms 
occur.  The  well  known  "reindeer  moss"  is  a  lichen.  For 
the  purpose  of  the  following  study,  one  of  the  gray  Parme- 
lias  (fig.  227a)  and  one  of  the  chimney  lichens  that  grow  on 
decaying  stumps  in  damp  woods  (fig.  2296)  will  answer  our 
needs. 


r"- 


a 


Fig.  227.  Lichens,  a,  a  common  encrusting  lichen,  showing  fruiting  cup- 
ules;  6,  a  "chimney  lichen."  whose  "chimneys"  are  covered  with  powdery 
white  lichen  buds  (soredia). 


392 


GENERAL  BIOLOGY 


Lichens  appear  as  single  organisms.  They  were  long  so 
considered.  It  is  convenient  to  describe  them  still  as  single 
species;  for  they  are  such,  for  all  practical  purposes.  But 
they  are  composite  species,  each  consisting  of  a  fungus  and 
an  alga,  living  together  in  structural  and  physiological 
union. 

The  form  of 
the  combina- 
tion is  domina- 
t  e  d  by  the 
fungus,  which 
develops  an  un- 
derlying strat- 
um for  attach- 
ment  to  the 
support,  and  a 
covering  cortical 
layer  having 
great  capacity 
for  resisting 
e^'aporation — of 
great  advantage 
in  exposed  situ- 
ations :  and  in 
its  more  porous 
open  fi  b  r  o  u  s 
middle  layer, 
shelters  a  host 
of  algal  cells. 
The  color  of  the 
latter  shows 
through  when  the  lichen  is  wet,  but  the  true  relations 
of  parts  are  best  made  out  by  cutting  vertical  sec- 
tions (fig.  229),  through  the  thallus,  and  examining  them 


Fig.  228.      A  strap  lichen  growing  on  a  tree  trunk  in 
damp  woods. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     393 


FiG.  229.  Vertical  sec- 
tion through  a  lobe  of 
acommon  lichen 
(Physcia  stellaris), 
showing  fruiting  sur- 
face above,  a,  spores 
of  the  fungus;  b,  b, 
algal  ceils,  held  among 
the  fungous  filaments, 
which  are  loosely  ar- 
ranged at  c,  but  com- 
pacted together  to 
rorm  protective  sur- 
face at  d.  (After 
Bessey). 


with  a  microscope. 
It  will  then  be  at 
once  apparent  that 
the  body  is  mainly 
a  complex  of 
branched  fungus 
filaments  and  that 
the  algal  cells  occu- 


pymg 


rjQ; 


the  middle 
stratum,  are  in  close  union  with  some  of 
these  filaments,  enwrapped  by  them, 
or  indented  by  blunt  protuberances 
from  them. 

This  union  is  for  mutual  benefit.  We 
have  already  learned  that  a  plant  like 
this  fungus,  lacking  chlorophyl,  cannot 
get  its  carbon  directly  from  the  carbon 
dioxide  of  the  air;  and  in  such  situa- 
tions, there  is  no  other  adequate  source 
of  supply.  Through  the  agency  of  the 
green  alga,  however,  and  by  means  of 
its  close  attachment  to  the  algal  cells,  it 
gets  carbon  made  up  into  assimilable 
form.  It  furnishes  the  alga  in  return 
shelter  and  protection  and  retains  about 
it  watery  solutions  containing  the  other 
materials  for  its  food.  The  algal  cells 
have  room  for  growth  and  division: 
alga  and  fungus  grow  together,  main- 
taining constant  relations,  resulting  in  a 
growth  habit  by  which  lichen  species 
are    known.     The    combination    is    an 

efficient  one  for  meeting  hard  conditions  of  life  in  drv  and 

sterile  situations. 


394 


GENERAL  BIOLOGY 


Some  species  that  live  symbiotically  can  be  cultivated 
apart ;  but  others  appear  to  have  become  so  fully  established 
in  this  manner  of  life  that  they  are  no  longer  able  to  live 
apart. 

There  are  other  cases  of  symbiosis  in  different  groups. 
We  have  already  seen  green  hydras;  the  color  is  due  to 
minute  algal  cells  (zoochlorellcE)  living  within  the  larger  cells 
of  the  hydra,  doubtless  using  there  the  carbon  dioxide  which 
the  hydra  cells  excrete,  and  giving  them  back  again  the 
liberated  oxygen  for  respiration.  Attached  to  the  roots 
of  beech  tree  s  are  molds  that  do  for  the  tree  the  absorbing 
work  ordinarily  performed  by  rhizoids,  while  the  tree  sup- 
plies them  with  carbon  products.  Thus  here  also  the  benefit 
is  mutual. 

Sttidy  jo.     The  relations  of  fungus  and  alga  in  the  lichen. 

Materials  needed:  Lichens  of  the  two  types  shown  in 
figure  227,  the  foliose  one  with  spore  cupules  (apothccia) 
developed.    Razor  and  pith  for  cutting  sections. 

Place  a  cupule-bearing  thallus  between  two  wet  pieces  of 
pith,  and  cut  vertical  sections  as  thin  as  possible  wdth  a 
razor.  Mount  and  examine  a  number  of  these  and  select 
the  best  for  study. 

Mark  the  general  arrangement  and  distribution  of 
fungus  and  alga.     Then  study  the  fungus: 

i)   The  form  of  its  filaments  in  the  several  layers. 

2)  The  form  of  its  fructification  in  the  cupule;  compare 
with  an  account  of  the  Ascomycetes,  in  any  good  text -book 
of  botany. 

Then  study  the  alga.  To  do  this  remove  the  cover,  tease 
the  algal  layer  of  a  section  to  bits  on  a  slide,  cover  again, 
and  study  the  alga  in  the  fragments.  Determine  the  rela- 
tions to  the  algal  cells  of  the  investing  fungus  filaments. 
Look  for  evidences  of  division  in  the  algal  cells. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT      395 

Scrape  a  little  of  the  whitish  powdery  substance  covering 
the  surface  of  the  chimney  lichen,  and  mount  it  on  a  slide  in 
water;  spread  it  out  thin  by  pressure  (with  rotation)  upon 
the  cover  glass,  and  study  the  dissociated  fragments.  These 
should  be  little  groups  of  algal  cells  intertwined  with  fungus 
filaments — lichen  buds  (soredia):  in  short,  minute  lichens, 
ready  for  dispersal.  Obviously,  when  the  spores  of  the 
fungus  upon  germination  have  to  find  and  attach  themselves 
to  the  proper  algal  cells  there  are  some  exigencies  to  be  met 
that  are  obviated  by  this  method  of  starting  new  plants 
by  means  of  soredia. 

The  record  of  this  study  may  well  consist  in  some  diagrams 
and  drawings  of  the  facts  demonstrated. 


Fig.   230.      Nest   of    song   sparrow    containing  three    sparrow   eggs   and   one 
cow  bird  egg.      Photo  kindly  loaned   by    Professor  C.  H.  Eigenmann. 


396 


GENERAL  BIOLOGY 


2.   Parasitism. 


Parasitism  is  a  relation  between  two  species  that  costs  the 
one  its  substance  and  the  other  its  independence;  the  one 
species  is  called  host,  the  other  parasite. 

The  cost  to  the  host  species  may  be  light  or  severe, 
according  to  the  extent  of  the  parasitism.  It  is  compara- 
tively light  in  such  case  as  that  of  the  song  sparrow  that 

hatches  the  cow-bird's  ^'g'g.  The 
latter  is  parasitic  only  to  the  ex- 
tent of  the  rearing  of  her  brood. 
She  deposits  her  ^gg  in  the  nest  of 
the  sparrow  (as  shown  in  figure 
230),  supplanting  a  sparrow  ^gg 
for  the  purpose,  and  leaves  it 
there  for  the  sparrow  to  hatch,  and 
to  feed  through  the  nesting  period. 
The  cost  to  the  host  species  may 
amount    to    personal    discomfort 


Fig.  231.  Downy  flower  gall 
of  the  goldenrod.  h,  a  gall 
ami  a  flower  head:  i,  a  double 
gall  split    open,    showing   the 

^S,?1hi^;;pf='o"T'ofrlc"oni3)    merely,  as  in  the  case  of  many 

parasite  in  the   other   (right 
hand)  chamber. 


small  external  and  internal  para- 
sites of  the  larger  mammals — lice, 
fleas,  ticks,  worms,  etc. — or  it  may  amount  to  loss  of  strength 
or  even  oi  life  of  many  individuals.  The  host  may  be  eaten 
by  degrees  by  a  single  large  parasite,  as  is  the  midge  that 
makes  the  downy  flower  gall  of  goldenrod  when  parasitized 
by  the  braconid  shown  in  fig.  231 ;  or  it  may  be  eaten  by  a 
large  number  of  smaller  parasites,  as  is  the  caterpillar  shown 
in  fig.  232.  In  any  case  parasitism  is  the  burden  of  the  host 
species;  but  the  manner  of  life  of  the  host  is  little  altered 
thereby. 

vSuch  is  not  the  case,  however,  with  the  parasite,  which, 
according  to  the  nature  and  extent  of  its  dependence  upon 
the  host  species,  becomes  always  more  or  less  degenerate. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIROXMEXT     397 


•  TLf  >t ''//f 


>^ 


ip 


The  cowbird,  relieved  of  the  care  of  her  young,  has  lost  her 
nesting  instincts.  The  Indian  pipe  (fig.  233)  attached  to 
the  roots  of  trees  whence  it  can  draw  manufactured  carbon 
products,  has  lost  its  green  color  and  its  leaves.     Sacculina, 

that  famous  illus- 
tration of  the  degen- 
eracy that  results 
from  the  parasitic 
habit,  living  in  the 
the  perfect  nurture 
and  shelter  afforded 
by  its  crab  host, 
has  lost  all  those 
structures  and 
capacities  by  which 
we  recognize  its  free 
living  kindred. 

In  general  it 
may  be  said  that  in 
proportion  as  the 
conditions  of  living 
become  simple, easy 
and  secure,  the 
parasite  comes  to 
lack  those  organs 
and  faculties  necessary  to  meet  hard  conditions,  in  battling 
with  which  they  were  developed.  This  loss  is  not  the  result 
of  the  parasitic  habit,  but  of  the  sheltered  life  that  goes  with 
it.  The  series  of  insect  larvae  we  have  used  to  illustrate 
metamorphosis,  excellently  illustrates  degeneracy  also, 
though  none  of  the  larvse  used  was  parasitic.  It  would  not 
be  difficult  to  select  parasitic  insect  larvae,  that  would 
constitute  parallel  degeneration  series.  It  seems  clear  that, 
as  in  the  individual,  so  in  the  long  run  in  the  race,  it  is 
effort  that  builds;  disuse  leads  to  degeneration. 


Fig.  232.  A  parasitized  moth  larva  on  blue  grass 
top:  some  of  its  parasites  ha\e  spun  their  cocoons 
beside  it,  others  on  the  grass  blade  above;  b, 
shows  an  easy  miethod  of  getting  the  adult  para- 
sites from  the  cocoons. 


398 


GENERAL  BIOLOGY 


The  two  primal  functions  of  feeding 
and  reproduction  not  even  the  parasite 
may  lose;  on  the  contrary  it  often 
develops  improved  feeding  apparatus 
and  increased  reproductive  capacity; 
sacculina  has  done  so;  and  the  liver 
fluke,  which  is  parasitic  on  two  hosts, 
snail  and  sheep,  at  different  stages  of  its 
existence  has  developed  an  extraordinary 
reproductive  capacity  to  meet  the  exi- 
gencies of  shifting  from  one  host  to  the 
other. 

Parasitism  may  be  either  external  or 
internal,  temporary  or  permanent,  at  one 
stage,  or  during  the  whole  life  of  either 
host  or  parasite,  on  the  part  of  the  female 
only  (in  its  incipiency,  the  female  seek- 
ing shelter  for  her  brood)  or  on  the  part 
of  both  sexes. 

Parasitism  is  one  of  many  possible 
shifts  for  a  living.  The  opportunities 
for  it  have  lain  in  the  accumulation  of 
stores  of  rich  organic  products  on  the 
part  of  the  larger  organisms.  These  are 
available  only  to  smaller  species.  Hence 
parasitism  is  a  prevalent  habit  mainly 
among  the  smaller  organisms.  The 
larger  parasites  offer  like  opportunities 
for  smaller  ones,  and  are  themselves 
parasitized.  The  common  bittern  has 
Fig.  233.  Indian  as  an  extcmal  parasite  the  fly  shown  in 
siiic'fl^ow^erin?piant"    fig.  2 3 4,  living  among  its  feathers.  The  fly 

has  its  ow^n  external  parasites — the  mites 
show  in  the  figure,  clustered  at  the  joints  of  the  legs,  where 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     399 


thin  connecting  membranes  offer  a  point  of  attack.  Es- 
caping from  the  pressure  of  competition, and  from  the  attack 
of  enemies,  a  few  of  the  smaller  representatives  of  many 

groups  have  become  parasites. 
In  those  groups  of  the  Hymenop- 
tera  that  are  most  extensively 
addicted  to  the  parasitic  habit, 
primary  parasites  are  commonly 
followed  by  secondary  parasites, 
(hyperparasites) ,  and  these  occa- 
sionally by  tertiary  parasites, 
the  difference  in  size  between 
host  and  parasite,  being  here  at  a 
minimum. 

Parasites  are  nature's  agents 
for  regulating  the  natural  balance . 
They  prevent  the  undue  increase 
of  any  species.  They  are  them- 
selves self  regulating;  for  with 
their  own  undue  increase,  they 
eliminate  themselves  by  eliminat- 
ing their  own  food  supply. 

In  recent  years  the  aid  of  parasites  has  been  sought  to 
stay  the  ravages  of  noxious  species,  like  the  gypsy  moth. 
Sometimes  they  are  imported  for  this  purpose;  in  which 
case  care  is  taken  to  leave  their  hyper-parasites  behind. 

A  moment's  reflection  upon  the  facts  that  have  been 
before  us  in  this  course  will  make  it  clear  that  parasitism  is 
by  no  means  sharply  distinguished  from  other  phenomena  of 
dependence  of  one  individual  upon  another.  It  is  living 
upon  the  living,  plant  upon  plant,  animal  upon  animal,  one 
species  upon  another,  that  we  call  parasitism.  That  the 
boundary  between  symbiosis  and  parasitism  is  not  hard  and 
fast  is  shown  by  the  case  of  the  nematode  that  lives  in  the 


Fig.  234.  A  parasitic  fly 
(Olfersia)  that  lives  among 
the  feathers  of  the  bittern, 
bearing  clusters  of  parasi- 
tic mites  at  the  joints  of  its 
own  body  and  legs. 


400  GENERAL  BIOLOGY 

body  cavity  of  the  earthworm  (cited  in  chap.  Ill,  p.  178). 
Ordinarily,  nematodes  found  in  such  situation  are  parasites, 
but  here  they  are  found  clearing  up  the  lumps  of  waste 
chloragogue — impedimenta  to  the  worm — accumulated  in 
the  hinder  segments,  and  the  relation  seems  to  be  one  of 
mutual  advantage.  Were  the  two  species  mutually 
dependent  in  this  function,  we  should  call  it  symbiosis.  As 
it  is  we  call  it  commensalism,  and  say  that  the  nematode  is  a 
guest,  and  not  a  parasite.  Commensalism  may  well  have 
been  at  times  a  transition  stage  in  the  development  of  para- 
sitic habits. 

Study    ^i.     A     comparative     examination    of    a    series    of 

parasites  of  a  single  order. 

Materials :  As  good  a  series  of  specimens  for  comparison 
as  may  be  had  in  any  favorable  group ;  flowering  parasitic 
plants;  copepods,  crabs,  worms,  etc.  Hosts  may  be  dis- 
regarded. 

Compare  together  as  to: 
Organs  of  feeding. 
Organs  of  reproduction. 
Organs  of  locomotion. 
Organs  of  sense  perception. 
Compare  males  and  females  of  each  parasite  if  possible  as 
to  degree  of  degeneracy. 

Compare  together  young  larval,  and  adult  forms  of  the 
more  completely  parasitic  species  selected  for  study. 

The  record  of  observations  should  be  preserv^ed  in  notes 
and  sketches. 

J.     Pollen  Distribution. 

In  our  study  of  the  green  plant  series  (Chapter  III),  we 
have  seen  how  the  motile  sperm  cells  of  the  primeval 
aquatic  plant  gradually  lost  their  opportunity  for  swimming 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     401 


to  meet  the  ovum,  as  plants  became  terrestrial  and  grew  to 
larger  size.  The  distances  to  be  traversed  in  order  to  accom- 
plish fertilization  became  greater  and  the  route  lay  through 
the  air;    transportation  became    necessary;    and    it   came 

about  that  the  carriage  of  the 
microspore,  and  not  of  the  naked 
sperm  cell,  was  the  plan  that  suc- 
cessfully met  the  difficulties  of 
the  situation. 

Flowering  plants  were  sur- 
rounded by  various  means  of 
transportation  for  their  pollen. 
Two  of  these  were  of  prime  im- 
portance; the  wind  and  winged 
insects.  The  w4nd  had  certain 
great  advantages.  It  could  be 
be  depended  on  to  blow  at  all 
seasons,  night  and  day,  and  if 
pollen  were  light  enough,  to  sift 
it  everywhere,  and  to  deposit 
some  of  it  in  the  right  place  for 
cross  fertilization.  But  on  the 
other  hand,  it  was  quite  indis- 
criminating  as  to  where  it  should  blow,  and  very  wasteful 
of  pollen  in  consequence.  Winged  insects  on  their  part, 
having  a  liking  for  the  nectar  of  flowers,  would  fly  from 
flower  to  flower  with  great  precision,  and  if  only  the  flower 
could  adjust  itself  to  profit  thereby,  would  distribute  the 
pollen  with  far  less  waste.  But  their  aid  was  less  trust- 
worthy, and  might  at  any  time  prove  inadequate;  they 
were  liable  to  casualties  of  storm  and  pestilence.  Their 
very  power  of  selection  might  lead  them  to  neglect  one 
species  for  others  more  attractive.  And  their  aid  was 
most  needed  by  species  of  sparse  distribution. 


Fig.  235.  Black  oak  flowers, 
m,  a  single  pistillate  flower;  n, 
a  single  staminate  flower,  be- 
fore the  bursting  of  the  anthers. 


402 


GENERAL  BIOLOGY 


We  have  learned  from  the  studies  in  Chapter  I  to  what 
extent  our  common  plants  have  become  adapted  to  insect 
aid  in  pollen  transference,  and  how  greatly  they  have  become 
modified  in  special  adaptation  thereto.  We  are  now  to 
study  comparatively  the  results  in  pollen  production  of 
adaptations  to  all  the  various  means  of  securing  fertilization 
including  water  flotation  of  the  pollen  of  submerged  aqua- 
tics that  bloom  at  the  surface,  and  the  automatic  self 
pollinating  acts  of  flowers  themselves. 

Sttidy  52.     Pollen  production  as  affected  by  its  mode  of 

distribution. 

Materials  needed:     Flowers  of  the  nine  sorts  indicated 
below : 

I.    Tree,   such  as  oak  (fig.  235),  hickory, 


Wind 
pollinated. 


Insect 
pollinated 


box  elder  or  hornbeam. 

2 .  Herb, such  as  meadow  rue,  grass  or  sedge. 

3.  A  large  open  solitary    flower  such    as 
trillium  or  may -apple. 

4.  An  open,  loosely  chistered  flower,  such 
as  spring  beauty,  or  buttercup. 

5.  A   highly  specialized   bilateral    flower, 
such  as  the  wood  betony  or  sweet  pea. 

6.  A  composite  flower,  such  as  the  dande- 
lion (fig.  236). 

Water  pollinated.     7.  A  river  weed  (Potamogeton) . 

8.  Open,  chickweed    (Stellaria  media)   or 
door  weed  (Polygonum). 

9.  Clistogamous,  the   blue    violet    {Viola 
cucullata) . 

All  these  will  be  obtainable  anywhere  in  spring,  except 
numbers  7  and  9,  both  of  which  may  be  used,  preserved  in 
alcohol.  The  clistogamous  flowers  of  the  violet  may  be 
found  through  the  whole  summer  after  the  blue  flowers  have 


Self 
pollinated 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     403 

ceased  to  appear  see  figure  27,  on  page  35.  The  function  of 
these  has  been  discussed  on  page  34. 

Study  these  individually,  and  write  their  characters  with 
which  we  are  now  concerned  in  a  table  prepared  with  the 
following  column  headings: 

Name. 

Sex  (male,  female  or  bisexual). 

Form  of  flower  cluster. 

Number  of  stamens  per  flower. 

Number  of  pistils  per  flower. 

Number  of  pollen  grains  per  stamen. 

Number  of  ovules  per  carpel. 

Ratio  for  the  whole  plant  of  pollen  grains  to  ovules. 

The  labor  of  making  this  table  chiefly  consists  in  counting 
the  pollen  grains  in  anthers  of  the  nine  species  selected. 
The  number  of  ovules  will  usually  be  found  stated  in  the 
larger  works  on  systematic  botany,  and  these  may  be  used 
for  reference.  Since  there  are  some  slight  difficulties  of 
manipulation  to  be  encountered,  it  may  be  well  to  suggest, 
how  to  proceed. 

Get  anthers  for  pollen  counting  from  unopened  buds,  in 
order  that  the  previous  shedding  of  some  of  the  pollen  may 
not  vitiate  the  count.  Select  anthers  of  average  size,  or, 
better,  count  several  and  average  the  result. 

Large  anthers,  like  those  of  trillium,  should  be  divided, 
say  into  eighths,  and  a  part  taken.  This  is  easily  done  by 
placing  the  anther  flat  on  a  slide  and  pressing  the  edge  of  a 
scalpel  into  it  with  a  rocking  motion,  being  careful  to  make 
approximately  equal  successive  divisions.  Then  select  an 
average  segment,  expose  its  pollen  fully,  cover  and  count, 
and  multiply  to  get  the  whole.  Very  small  anthers,  like 
those  of  the  dandelion,  are  likely  to  be  quite  transparent, 
and  need  only  to  be  mounted  and  covered,  and  their  pollen 
content  may  be  counted  at  once.     It  will  be  necessary  to 


404 


GEXERAL   BIOLOGY 


Split  the  anther  tube  of  the  dandelion,  and  spread  it  out  flat 
before  covering  (fig.  236).  When  the  pollen  cavities  are  so 
filled  that  they  appear  dark,  a  little  pressure  on  the  cover 
will  often  burst  them  and   scatter  the   pollen,   so  that  it 

may  be  counted. 

The  gist  of  this  study  is 
in  the  ratios  of  the  last 
column.  For  ready  com- 
parison they  should  be 
reduced  to  the  form  x:i. 

With  perfect  flowers  the 
ratio  of  pollen  grains  to 
ovules  produced  will  be  the 
same  for  the  w^hole  plant  as 
for  the  single  flower,  but 
with  monoecious  (fig.  235) 
and  dioecious  species  it  will 
be  necessary  to  count  and 
estimate  for  equivalent  pro- 
portions of  the  total  of  male 
and  female  inflorescence. 

The  record. — In  conclu- 
sion,   ascertain    from    the 

^;,sroTbt^'ietXovuie'case?"  *■'"''■     f^CtS     of      the      Completed 

table  whether  the  form  of 
the  cluster  or  the  manner  of  flower  aggregation  in  it  have 
had  any  effect  on  the  amount  of  pollen  produced. 


Fig.  236.  A  single  dandelion  removed 
from  the  flower  head.  /,  stigma;  k, 
the  anther  ring,  split  and  unrolled  at  o, 
the    separate    filaments   shown   at    p 


III.        ADJUSTMENT     IN     FORM     AND     APPEARANCE. 

When  we  have  gotten  to  this  division  of  our  subject,  it  has 
already  been  illustrated  in  manifold  ways  by  the  organisms 
we  have  had  before  us.  Nevertheless,  it  will  still  repay  a 
more  careful  examination. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     405 

There  is  the  adjustment  of  the  individual  to  external 
conditions,  and  there  is  the  adjustment  of  the  race.     The 


Fig.  237.    Cross-section  of  an  elm  bough   with  its  history  written  in  its  wood 
rings. 

former  is  familiar  to  our  experience.     The  tanning  of  the 
skin  with  exposure  to  the  sun,  the  strengthening  of  the 


4o6  GENERAL  BIOLOGY 

muscles  through  use,  acclimation,  immunisation;  these  and 
many  others  are  every  day  illustrations  of  the  response  of 
the  individual  to  conditions  of  environment.  Figure  237 
shows  the  record  in  wood  of  a  series  of  successive  responses 
on  the  part  of  the  bough  of  an  elm  tree  during  the  2  5  years 
of  its  life.  The  five  dark  rings  in  the  center  represent  the 
first  five  years  of  erect  growth  (18 7 8-1 8 8 2),  w^hile  it  was  still 
near  the  top  of  the  tree,  and  abundantly' and  symmetrically 
Hghted.  It  started  in  1878  from  a  bud  formed  on  the  west 
side  of  the  top  shoot  of  a  three  year  old  sapling.  The 
twelve  close  set  rings  following  represent  the  scanty  growth 
of  the  next  twelve  years  (1883- 1894),  during  which  it  was 
struggling  for  light  beneath  the  higher  branches  that  had 
overtopped  it.  The  larger  growth  ring  for  1888  represents 
the  result  of  a  windy  season,  when  the  tossing  about  of  the 
upper  branches  allowed  this  one  to  get  more  light.  During 
this  time  the  bough  was  leaning  slightly  to  westward,  as 
indicated  by  the  greater  thickness  of  the  rings  on  that  side — 
the  lower  side  in  the  figure.  The  ensuing  sudden  unilateral 
enlargement  of  the  rings  was  due  to  an  accident.  Some 
children  climbing  in  the  tree  bent  this  bough  down,  and  left 
it  in  a  somewhat  drooping  position.  Thus,  it  was  brought 
out  from  the  shadow  into  the  light  again,  and  the  rapid 
growth  that  followed  was,  in  consequence  of  its  position,  on 
the  under  side  of  the  bough  at  the  bend  where  this  section 
was  made.  It  will  be  observed  that  for  four  years  (1895- 
1898)  the  addition  of  woody  tissue  was  bilaterally  sym- 
metrical upon  the  lower  side.  Then  another  accident 
changed  the  stress  upon  it  and  caused  it  to  grow  obliquely. 
It  chanced  to  overhang  a  walk,  and  in  the  spring  of  1899  to 
correct  its  drooping  it  was  hung  up  lightly  on  a  wire  at- 
attached  to  a  fork  above  and  a  little  to  one  side.  The  pull 
was  to  the  northward  during  the  ensuing  four  years  (1899- 
1902),  and  this,  assisted  by  prevailing  south-west  winds, 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     407 

caused  more  woody  tissue  to  be  formed  on  that  side.  In 
the  winter  of  1 90  2,  the  bough  was  cut,  and  its  autobiography 
was  interpreted  with  the  aid  of  competent  testimony  that 
was  still  available. 

Our  practical  studies  shall  be  of  the  modifications  of  form 
and  appearance  that  belongs  to  racial,  and  not  to  indi- 
vidual history. 

I.     The  re-adaptation  of  insects  to  aquatic  life. 

It  seems  now  quite  clear  that  insects  were  primitively 
terrestrial.  They  are  covered  with  a  tough  chitinized  skin, 
well  adapted  to  resist  evaporation.  They  are  provided 
with  a  respiratory  apparatus  of  distinctively  aerial  type. 
They  breathe  through  open  spiracles,  that  lead  to  inter- 
communicating air  tubes  (tracheae)  within  the  body.  As 
adults,  they  all  breathe  free  air,  and  are  adapted  only  by 
secondary  makeshifts  to  aquatic  life.  It  is  only  the 
larvae  of  scattering  groups  that  have  become  properly 
aquatic,  and  able  to  breathe  the  air  that  is  dissolved  in  the 
water — all  the  larvae  of  a  few  small  groups,  and  scattering 
members  of  most  of  the  larger  orders.  Among  these, 
therefore,  we  should  be  able  to  see  the  result  of  the  fittinsr 
of  diverse  forms  to  the  new  conditions. 

When,  with  the  luxuriant  development  of  the  insect 
group,  the  press  of  life  on  land  crowded  some  insects  back 
into  the  water,  the  problem  of  getting  air  was  the  chief  one 
to  be  encountered.  Its  full  solution  lay  in  the  development 
of  suitable  respiratory  apparatus.  An  impervious  chiti- 
nized skin  perforated  by  open  air  tubes  stood  in  the  way  of 
ready  re-adaptation.  Adult  insects  merely  adopted  various 
devices  for  carrying  or  otherwise  obtaining  free  air  when 
in  the  water, without  altering  their  mode  of  respiring  it: 
many  insect  larvae,  also,  get  their  air  supply  only  at  the 
surface  (fig.  238).     But  the  softer  and  more  plastic  larvae, 


4o8 


GENERAL   BIOLOGY 


■'(riH 


'mii^^iiih^^ 


thin  skinned  and  permeable,  are  able  to  get  oxygen  from 
the  water,  and  have  become  strictly  aquatic. 

Among    aquatic   insect   larvae    (properly    so-calledj    are 
found  three  respiratory  types: 

1 .  Those  without  gills. 
These  are  minute  larvae, 
like  those  of  the  biting 
midges  (Ceratopogon,  fig. 
239)  that  live  in  floating 
masses  of  filamentous 
algae,  where  liberated 
oxygen  is  abundant,  or, 
if  of  larger  size,  as  in  the 
case  of  some  stoneflies 
(Perlidae)  they  live  in 
rapid  and  well  aerated 
water.  The  larger  of 
these  although  lacking 
gills  have  an  abundant 
development  of  fine  air 
tubes  in  the  thin  mem- 
branes joining  the 
thoracic  segments  of  the 
body  on  the  ventral 
side. 

2.  Those  with  blood 
gills. — These  most  nearly  approximate  aquatic  vertebrate 
larvae  in  their  mode  of  respiration.  Blood  gills  are 
protrusions  of  the  body  wall  through  which  the  blood 
flows;  the  exchange  of  gases  in  respiration  takes  place 
between  the  blood  inside  and  the  water  without.  Blood 
gills  are  developed  in  many  dipterous  larvae,  and  oftenest, 
about  the  posterior  end  of  the  alimentary  canal  (fig  239^). 
In  dipterous  larvae  the  tracheae  are  often  somewhat  reduced. 


Fig.  238.  The  larva  of  a  swale  fly  {Sepedon 
fuscipennis).  a.  Pulling  away  from  the 
surface  film,  the  guard  hairs  surrounding 
the  breathing  pores  convergent  at  tips;  b, 
end  of  body  as  seen  when  resting  on  the 
surface,  hairs  outspread. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     409 

3.  Those  with  tracheal  gills. — These,  comprising  the 
larger  larvae  of  all  the  more  generalized  orders  of  aquatic 
insects,  have  adhered  more  strictly  to  the  tracheate  type  of 
respiratory  apparatus.  Tracheal  gills  are  protrusions  of  the 
body-wall  with  fine  tracheal  tubes  grown  out  into  them,  and 
the  exchange  of  gases  in  respiration  is  between  the  air  in  the 
tubes  and  the  water  outside  the  gill.  The  tracheal  system, 
therefore,  instead  of  being  reduced,  is  increased  by  the  out- 
growth of  the  additional  parts  that  penetrate  the  gills. 


Fig.  239.     Larvae  of  dipterous  insects,     x,  the    pnnkie  {Ceratopogon).     y  ,  the 

phantom  larva  of  Corethra;     s,    a     "blood   worm" — ihe   larva  of   a   midge 

{Chironomus) ;/,  floats  (expansions  of  the  main  air  tubes) ;  g,  g.  g,  blood  gills. 


Tracheal  gills  may  be  external  as  in  the  case  of  the  damsel- 
fly  nymph  shown  in  fig.  225,  or  internal,  as  in  the  case  of  the 
larger  dragonfly  nymph  shown  in  figure  240.  Whatever 
their  position  number  or  arrangement,  they  conform  more 
or  less  closely  in  shape  to  two  types,  filiform  or  cylindric,  and 
lamelliform  or  flat. 

Their  diversity  in  form,  position,  arrangement  and  num- 
ber and  size  will  be  seen  in  the  series  of  larvae  selected  for 
study. 


4iO 


GENERAL   BIOLOGY 


External 


Study  5 J.     A  preliminary  examination  in  living  specimens 
of  the  principal  gill  types  of  aquatic  insects. 

Materials  needed :     Living  larvae  to  illustrate : 

1.  Blood  gills  (larvae  of  Culex,  the  mosquito,  Corethra  or 
Chironomus). 

2.  Tracheal  gills: 

j  Filamentous  (larvae  of  a  caddis  fly,  etc.) : 
I  Lamellif  orm  (nymphs  of  a  damselfly  or  mayfly) . 
Internal  (nymphs  of  the  dragonfly,  Libellula). 

Mount  a  larva 
having  blood  gills  in 
a  copious  supply  of 
water,  cover  and 
study  the  gills 
directly,  noting  their 
number, position  and 
relations.  Focus 
carefully  upon  one 
gill  to  see  the  outline 
of  its  internal  cavity, 
and  to  see  the  leuco- 
cytes that  drift  about 
in  it. 

To  study  the  ex- 
ternal tracheal  gills, 
snip  off  a  few  gills 
with  fine  scissors 
and  mount  them  in 
water ;  cover  and 
examine  at  once, 
to  see  the  tracheoles  before  the  penetration  of  the  water 
into  them  has  rendered  these  invisible.  While  filled  with 
air  they  appear  as  sharply  defined   black   lines.     They   are 


/ 


/ 


Fig.  240.   Dragonfly  nymph  {Celithemis  eponina). 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     411 

not  visible  in  preserved  specimens;  hence,  living  larvae 
must  be  had  for  this.  Study  especially  the  division  of  the 
large  tracheae  into  fine  tracheoles  and  the  disposition  of 
the   latter    and   their    intercommunications. 

The  internal  gills  of  a  dragonfly  (fig.  241)  are  arranged  in 
rows  upon  the  inner  walls  of  a  gill  chamber,  made  out  of  the 
posterior  third  of  the  alimentary  canal.  It  is  so  fine  a  piece 
of  respiratory  apparatus,  so  unique  in  plan  and  it  exhibits 
such  delicacy  and  refinement  of  structure  it  is  well  worth 
a  careful  examination. 

It  will  be  well  first  to  see  the  external  evidences  of  its 
operation.  Regular  respiratory  movements  of  the  abdomen 
can  usually  be  seen  in  a  nymph  that  lies  quietly  in  a  shallow 
dish  of  water.  They  may  often  be  seen  intensified  if  the 
nymph  be  turned  over  on  its  back.  With  the  expansion  of 
the  abdomen  water  is  slowly  taken  in  through  the  anal 
aperture  to  be  expelled  with  its  contraction.  The  currents 
of  the  water  may  be  demonstrated  by  placing  some  colored 
fluid  in  the  w^ater  close  beside  the  anal  opening.  This  is  best 
done  by  holding  the  point  of  a  copying  pencil  in  that  position 
until  its  color  is  imparted  to  the  water.  The  forcible  ejec- 
tion of  water  from  this  gill  chamber  as  an  aid  to  propulsion 
may  be  seen  while  the  nymph  is  swimming  about.  Some 
idea  of  the  force  of  the  expulsion  may  be  gained  by  tilting 
the  abdomen  of  a  swimming  nymph  upward  until  it  touches 
the  surface  of  the  water,  when  the  water  in  the  gill  chamber 
will  be  shot  into  the  air. 

To  study  the  structure  of  the  gill  chamber  and  of  the  gills 
themselves,  the  following  method  will  be  found  to  be  expedi- 
tious and  satisfactory.  Kill  the  nymph  by  snipping  off  its 
head.  Then  snip  off  the  abdomen  at  its  base ;  trim  off  its 
sharply  triangular  lateral  margins  for  its  whole  length;  pin 
it  down  to  the  waxed  bottom  of  a  dissecting  dish  that  is 
small  enough  for  use  on  the  stage  of  a  dissecting  microscope, 


412  GENERAL   BIOLOGY 

or  under  a  pocket  lens;  carefully  lift  off  the  roof  of  the 
abdomen,  (already  loosened  at  the  sides  by  the  trim-off  of 
the  margins,)  by  seizing  it  in  front  with  the  forceps. 

This  will  expose  the  gill  chamber,  which  occupies  the 
greater  part  of  the  abdominal  cavity,  and  terminates  the 
alimentary  canal.  The  severed  posterior  end  of  the  stomach 
will  be  seen  in  the  middle  in  front,  terminated  in  the  rear  by 
a  dense  cluster  of  nephridia  (Malpighian  tubules)  and 
followed  by  a  slender,  white,  ventrally  curved  and  much 
concealed  intestine,  joining  it  to  the  gill  chamber.  On 
either  side  of  the  stomach  will  be  seen  a  large,  silvery  white 
air  trunk,  which  breaks  up  posteriorly  into  a  great  brush  of 
lesser  branches  that  penetrate  the  walls  of  the  gill  chamber. 
This  chamber  itself,  will  be  somewhat  collapsed ;  it  may  be 
distended  by  injecting  air  or  water  through  the  anal  aper- 
ture with  a  fine-pointed  pipette;  its  longitudinal  extent 
may  be  seen  by  lifting  the  stomach  with  a  forceps  and 
drawing  it  forward.  If  turned  to  one  side,  a  ventral 
longitudinal  tracheal  trunk  may  be  seen  on  either  side  of 
the  body,  breaking  up  in  the  rear,  like  the  dorsal  trunk, 
into  a  multitude  of  branches,  and  entering  the  walls  of  the 
gill  chamber  from  below. 

Through  the  transparent  walls  of  the  gill  chamber  may 
be  seen  lines  of  the  black  pigment  that  occupies  the 
bases  of  the  internal  gill  plates.  Discovering  thus  the 
location  of  the  rows  of  gills,  the  chamber  may  be  safely 
opened  by  inserting  the  point  of  a  fine  scissors  and  cutting 
the  wall  for  its  entire  length  between  two  rows.  The 
circular  muscles  of  the  wall  will,  by  their  contraction  turn 
the  whole  organ  inside  out,  and  fully  expose  the  rows  of 
beautiful,  feathery,  purpHsh  tinted  gill  plates.  Then  if  a 
row  be  isolated  with  scissors  and  mounted  on  a  slide  in 
water,  a  few  individual  gills  may  readily  be  isolated  with 
needles  under  a  dissecting  lens,  covered,  and  studied  with 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     413 

a   microscope.     The   accompanying   figures    (fig.  241)   will 
assist  in  identifying  all  the  structures  present. 

The  record  for  this  study  may  be  in  the  form  of  sketches 
and  diagrams  of  the  respiratory  apparatus  studied. 


I miiiiti 


Fig.  241.  Diagram  of  the  gill  chamber  of  the  nymph  of  a  dragonfly  (Ana* 
Junius)  from  drawings  by  Miss  Elizabeth  Andrews,  a,  cross  section  of  the 
gill  chamber;  d,  d,  dorsal  tracheal  trunks;  v,  v,  ventral  trunks;  /,  tuft  of 
filamentous  gills;  m,  longitudinal  muscle;  b,  a  single  gill  filament,  showing 
tracheae  and  tracheoles. 


Study  ^4.      The    comparative    development    of   respiratory 
apparatus  in  aquatic  insect  larvce. 

Materials  needed:  Either  preserved  or  fresh  specimens 
of  larvae  of  the  following:  Ceratopogon,  or  some  other  gill- 
less  form  (perlid  or  trichopter  will  do  as  well) . 

I.  Two  or  more  dipterous  larvae  having  blood  gills  of 
different  sort:  Chironomus  (the  larger  "blood  worms," 
with   ventral  abdominal  gills)  and  Simulium  will  be  best, 


414 


GENERAL  BIOLOGY 


Fig.  242.     Nymph  of  a  stonefly 
(Perla). 


and  easiest  obtained,  (see  appen- 
dix). 

2.  A  typical  perlid  nymph 
(Perla,  Neoperla  or  Acroneuria) . 

3.  Any  of  the  larger  species 
of  mayflies. 

4.  Any  sialid  larva  (Sialis, 
Chauliodes,  or  Corydalis;  larvae 
of  the  whirligig  beetle  would 
answer  the  same  purpose. 

5.  A  caddis-worm  with  abun- 
dant development  of  gills. 

6  and  7.  Damselfly  and  drag- 
onfly,data  for  the  addition  of 
which  were  obtained  from  the 
preceding  study. 

Study  these 
seven  repre- 
sentativ  e 
forms  indi- 
vidually, and 


write  the  characters  with  which  we  are 
here  concerned  in  columns  in  a  table 
prepared  with  the  following  column 
headings: 

Name. 

Order  (of  Hexapoda). 

Gill  type  (blood  gill,  or  tracheal  gill). 

Number  (of  individual  plates  or  fila- 
ments) . 

On  w^hat  segments  (use  the  Roman 
and  Arabic  numerals  as  indicated 
in  fig.  10,  p.  17,  so  far  as  possible). 

Form  (filiform  or  lamellif orm) . 


Fig.  243.     The  larva 
of  an  orl  fly  {Sialis). 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     415 


Arrangement  (solitary,  in  clusters,  in  whorls,  etc. ;  give 
number) . 

r  as  to  movement  (stagnant,  quiet,  rapid,  torren- 
Water  <       tial,  etc.) 

(  as  to  oxygen  content. 

The  record  of  this  study  will  be  contained  in  the  completed 
table . 

2.     Phylo genetic  adaptation  in  diving  beetles. 

We  will  now  study 
the  adaptation  to  a 
changed  environment  of 
a  series  of  forms  of  com- 
mon origin.  For  that 
purpose  it  would  be  hard 
to  find  better  material 
than  that  furnished  by 
the  family  Dytiscidae  of 
diving  beetles  (fig.  244). 
Almost  any  permanent 
pond  will  furnish  a  num- 
ber of  forms  that  differ 
in  size  and  habit,  and 
that  exhibit  different 
ITgatuX  "^'"^'"^    ^^''^^    ^Coptotomus    ^egrecs    and    kinds    of 

specialization.      We  will 
study  the  adaptation  of  the  adult  beetles  to  pond  life. 

These  beetles  have  fully  retained  their  terrestrial  mode 
of  respiration.  They  take  in  air  through  abdominal 
spiracles  situated  on  the  back  of  the  abdomen,  underneath 
the  wing  covers.  They  have  merely  adopted  improved 
means  of  carrying  air  with  them  when  they  descend  beneath 
the  surface  of  the  water. 


Fig.     244. 
intern 


4r6 


GENERAL  BIOLOGY 


Their  chief  problem  has  been  locomotion;  how  to  get 
through  the  water  speedily,  in  order  to  capture  their  prey 
and  to   escape   from  their  enemies.     Becoming  adapted, 


Fig.  245.  Diagram  of  the  ventral 
aspect  of  a  divingheetle  (Coptotomus 
interrogatus)  a,  antenna;  b,  mouth; 
c,  c,  coxal  cavities  for  the  fore  and 
middle  legs;  d,  labial  palpi;  e,  eye; 
/,  maxillary  palpi;  g,  lateral  margin 
of  the  prothorax;  h,  epipleura  of 
the  wing  cover  (elytron);  ^',  pro=ter- 
nal  process;  /,  met  asternal  fork;  k, 
hind  coxa  with  /,  the  inner,  and  o, 
the  outer  lammae ;  p,  the  coxal 
process  and  q,  the  coxal  notch:  r, 
trochanter  of  the  hind  leg;  s.  femur; 
t,  tibia;  u,  tarsus  of  five  joints;  v, 
spurs  of  the  middle  tibia.  /,  2,  j, 
4,  5,  6,  ventral  abdominal  segments 
5<i,  st^,  sf^,  sterna  pro-,meso-.  and 
meta-thorax,  respectively. 


therefore,  to  progression 
through  the  water — a  medium 
fo  sufficient  density  to  offer 
considerable  resistance — they 
have  acquired  a  remarkable 
uniformity  of  appearance.  It 
would  be  hard  to  find  another 
large  family  of  organisms  all 
the  members  of  which  are  of 
so  nearly  the  same  shape. 
Whether  large  or  small,  they 
are  all  of  one  form — that, the 
form  of  a  submarine  boat — 
compact  and  evenly  contoured 
and  pointed  at  both  ends. 

It  is   generally  agreed  that 

the  ancestors  of  the  Dytiscidas 

were  ground  beetles,  more  or  less  like  the  existing  members 

of  the  family  Carabidae,of  which  Calosoma  (fig.  246)  is  a 


ADJUSTMENT  OF  ORGANISMS  TO  EXVIROXMEXT     417 


representative.  We  may  get  some  idea  of  the  nature  and 
extent  of  the  adaptative  changes  that  have  taken  place  with 
the  return  to  aquatic  life,  if  we  compare  such  a  form  as 
Calosoma  with  one  of  the  larger  D^'tisicidae  (fig.  244). 
Something  of  the  manner  of  life  of  the  diving  beetle  has 
already  been  seen  in  study  48.  Calosoma  is  built  for 
running  about  on  the  ground,  climbing  in  and  out  of  depres- 
sions, hiding  in  crevices;  hence  it  is  loosely  jointed  in  both 
body  and  legs,  roughly  contoured,  with  prominent  eyes,  and 
large  antennae  beset  with  sensory  hairs.  In  Coptotomus  all 
this  is  changed  .     The  body  is  compact,  rigid  and  pointed  at 

the  ends.  The  contour  lines  are 
reduced  to  smooth  curves.  The 
legs,  especially  the  hind  ones 
that  are  chiefly  used  in  swim- 
ming are  flat  and  oar  like,  com- 
pacted and  stiffened,  limited  in 
variety  and  specialized  in  kind 
of  motion.  Remote  as  is  the 
analogy,  we  may  see  some  like 
phenomena  if  we  compare 
vehicles  for  locomotion  on  land 
with  boats;  especially,  if  we  con- 
ground  beetle  "trast  the  great  variety  of  form  of 
sycophanta:  after  land  vchiclcs  with  the  great  Uni- 
formity in  shape  of  hulls  of  boats. 


Fig.  246.     A 
(Calosofna 
Bos). 


Study  j^.     A  comparison  of  the  structure  of  groiuid  beetle  afid 

diving  beetle. 

Materials  needed:  A  supply  of  specimens  of  one  of  the 
larger  Carabidae  (Calosoma,  Galerita,  etc.),  and  of  one  of  the 
larger  Dytiscidae  (D3rtiscus,  Cybister,  Acilius,  etc.). 

Let  this  study  be  a  detailed  examination  of  the  external 
structures,  first  of  the  ground  beetle,  and  then  of  the  diving 


41 8  GENERAL    BIOLOGY 

beetle,  omitting  mouth  parts  which  are  little  altered  in  rela- 
tion to  aquatic  life.  All  the  hard  parts  (sclerites)  of  the  body- 
armor  may  be  identified  with  the  aid  of  figure  245. 

The  purpose  of  the  study  is  the  gaining  of  some  notion  of 
what  are  primitive  and  what  are  specialized  conditions  in 
diving  beetles. 

Study  the  structure  of  the  diving  beetle  especially  with 
reference  to : 

i)  That  fitting  together  of  the  ventral  sclerites  of  the 
thorax  that  has  to  do  with  increasing  the  rigidity  of  the 
body. 

2)  That  fitting  together  of  wing  covers  with  each  other 
and  with  the  sides  of  thorax  and  abdomen  that  has  to  do 
with  making  a  secure  enclosure  for  the  retention  of  air  when 
at  the  bottom  of  the  pond. 

3)  That  consolidation  and  alteration  in  form  of  the  hind 
coxae  that  has  to  do  with  increasing  the  rowing  efficiency  of 
the  hind  legs. 

The  record  of  this  study  may  consist  of  a  brief  tabular 
statement  of  the  chief  structural  differences  between  the 
two  beetles  examined,  illustrated  with  diagrams  if  desired. 

Study  j6.     A  comparative  study  of  size  and  activities    of 

diving  beetles. 

Materials  needed:  Plenty  of  live  specimens  representing 
six  or  more  genera  of  Dytiscidae,  preferably  of  different 
sizes.  The  specimens  should  be  in  normal  condition ;  if  not 
freshly  collected,  they  should  have  been  properly  kept,  cared 
for  and  fed. 

Prepare  a  table  with  the  following  column  headings 
abbreviated  as  desired: 

Name  (if  unknown,  use  the  keys  and  figures  provided  in 
the  appendix). 


\ 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     419 

(      Length  in  millimetres  (most  easily  and  quickly 
Size  -{  taken  with  a  small  caliper  rule). 

Weight  in  grams  (weigh  each  species  on  a  deli- 
cate balance;  put  beetles  in  envelopes  made  of 
filter  paper,  which  will  take  up  the  water,  a  number 
at  a  time  of  the  smaller  species ;  weigh  in  envelope ; 
weigh  envelope  alone;  deduct;  divide  remainder 
by  number  of  beetles  weighed;  quotient  should  be 
the  average  weight) . 

Strokes  per  second.      (Set  a  metronome 
beating  half  seconds  and  count). 

Strokes  per  length  of  body  (measure  of 
the  efficiency  of  the  individual  stroke). 
Speed   per   second*. 
Swimming  (a?  determined  above). 
Walking  (judge  this  not  by  speed  alone, 
but  by  ability  to  get  up  on  feet  and  walk, 
using  the  joints  of  legs  and  feet). 
Jumping. 
Taking  flight. 
Dodging. 

The  record  of  this  study  will  be  contained  in  the  completed 
table,  which  should  show  clearly  the  great  differences  in 
the  powers  of  these  beetles,  that  underlie  their  super- 
ficial similarity. 


Swimming 


Relative 
excellence  t 


*Place  the  beetles,  one  species  at  a  time,  in  a  broad,  shallow 
dish  of  water,  and  lay  a  few  pieces  of  soft  wire  of  measured  lengths 
(5,  10  and  20  cm.)  on  the  bottom.  With  the  metronome  beating 
half  seconds,  watch  the  beetles  as  they  swim  about,  and  judge  by 
the  time  it  takes  them  to  pass  given  lengths  of  wire. 

t Expressed  numerically:  the  best  swimmer  as  i,  second  best  2, 
etc.,  written  in  the  columns.  All  these  but  the  last  (which  is  best 
seen  in  the  water)  may  be  easily  determined  by  placing  beetle  of 
all  the  species  used  together  on  a  sheet  of  paper  spread  out  on  as 
table  before  a  window.  Place  them  on  the  side  remote  from  the 
source  of  light,  and  they  will  travel  toward  the  light  according  to 
their  several  abilities,  walking,  jumping  and  flying. 


420  GENERAL   BIOLOGY 

Study  57.     Field  observations  on  diving  beetles. 

Apparatus  needed :  Dip  nets  and  beakers  or  other  small 
vessels  for  individual  use.  A  seine  may  be  useful  for  obtain- 
ing greater  numbers  of  the  larger  forms  that  live  farther 
from  shore   (Dytiscus,  etc.) 

If  the  student  will  carefully  gather  his  own  material  for 
the  studies  of  this  subject,  he  w^ill  see  much  that  is  of  interest 
in  the  manner  of  life  of  these  beetles,  and  some  things  that 
will  aid  in  understanding  the  structural  peculiarities  of  some 
of  them,  to  be  worked  out  later  (in  study  58).  It  must  not 
be  forgotten  for  a  moment  that  all  peculiarities  of  vital 
importance  are  related  to  environment. 

The  best  collecting  grounds  are  ponds;  small  ponds  if 
permanent,  even  though  they  be  shallow.  Few  beetles  will 
be  seen  anywhere  without  special  search  for  them;  a  few 
may  be  seen  rising  to  the  surface  to  take  air,  and  immediately 
descending  again.  It  will  require  careful  collecting,  and 
discrimination  as  to  species,  to  get  a  goodly  variety.  Begin 
by  "sweeping"  the  submerged  vegetation  at  the  farthest 
reach  of  the  net  for  the  larger  species,  and  work  gradually 
toward  shore.  The  smallest  species  (Bidessus,  etc.),  will 
be  found  right  at  the  edge  of  the  water,  and  will  be  obtained 
by  scraping  the  bottom  close  up  to  the  bank.  Learn  care- 
ful collecting:  for  it  is  a  most  important  part  of  the  education 
of  a  naturalist. 

Dip  up  and  examine  the  trash  that  lies  on  the  bottom; 
examine  also,  floating  vegetation. 

Note  the  favorite  location  of  each  species:  the  center  of 
its  abundance.  Observe  the  relation  between  size  of  the 
species  and  the  depth  of  the  water  dwelt  in .  Observe  how  the 
jumping  species  gather  about  floating  trash,  which 
furnishes  a  support  from  w^hich  a  jump  in  the  air  can  be 
made.  Such  things  are  best  seen  before  the  water  has 
been  too  much  disturbed  with  nets. 


ADJUSTMENT  OF  ORGANISMS  TO  EWIROXMEXT      421 

Separate  out  the  species  in  suitable  receptacles  for  keep- 
ing alive.  Remember  that  all  are  carnivorous,  and  that  the 
larger  ones  if  pressed  by  hunger  may  eat  the  smaller; 
remember  also  that  all  can  climb  and  fly,  and  cover  vessels 
accordingly. 

The  record  of  this  study  may  consist  in  a  diagram  on  the 
plan  of  the  left  hand  side  of  fig.  224  on  page  385,  with  the 
names  and  places  of  all  diving  beetles  collected  indicated 
therein. 

Study  §8.     The  adaptive  structures  of  diving  beetles. 

Materials  needed :  Preserved  specimens  of  the  same 
species  used  in  the  preceding  study. 

Study  these  species  one  by  one,  and  record  the  more 
obvious  characters  called  for  in  a  table  prepared  with  the 
following  column  headings : 

Name. 

Sculpture  (development  of  furrows  or  structural  ornamen- 
tation, especially  of  the  back). 

Vesture  (development  of  hair  on  the  body,  especially  of 
the  back). 

Scutellum  (visible  or  hidden). 

(  Femur:    ] 

Relative  length     <  Tibia:       >  expressed  in  ratio  7:x:y 

(^Tarsus.    J 

^       .1-1       .        •       r  '  \  Oi^  what  legs  developed 

Specialized  swimming  fringes    <  -r,  ,   , .  „ 

^  o         o        j  i^eiative  excellence 

r  Number  (one  or  two) 

Claws  <  Equality  (equal  or  unequal) 

(  Mobility  (fixed  or  movable) 

Special  braces  (such  as  the  lobe,  x,  of  the  femur,  showm 
in  figure  285  on  page  524,  which  serves  to  steady  the 
action  of  the  tibia,  and  to  keep  it  moving  in  one  plane: 
developed  where  on  legs). 


42  2 


GENERAL   BIOLOGY 


CONCLUDING    WORK. 

As  a  conclusion  to  the  foregoing  studies,  make  a  tabular 
statement  of  the  adaptive  structures  observed  (a  few  are 
stated,  as  examples)  after  the  following  plan: 

Special  adaptations  of  diving  beetles. 

Best    de 

veloped 

in 


Of  head 
and  body 


Character 


^x  .-Flattening 
down  of  the 
eyes 


Telescoping 
of  head  by 
prothorax, 
etc. 


Of  appen- 
dages 

Of  vesti- 
ture 


Upward 
bending  of 
hind  legs,  etc. 

(  Loss  of  sen- 


Cybister 


Acilius 


Of  what 
advantage 


Dimished 
resistance 
to  water 


Better 

rowing 

position 


Involving 

what 
limitations 


Dimished 

range  of 

vision 


Poorer 
walking 
position 


<  sory  antennal 
(^  hairs,  etc. 

The  record  of  this  and  the  consummation  of  several 
preceding  studies  will  appear  in  the  last  table. 

J.     Animal  coloration. 

We  come  now  to  the  examination  of  characters  that  are 
more  superficial,  more  variable,  more  plastic,  and  that 
ordinarily  show  the  most  remarkable  fitness  to  environ- 
ment. We  pass  by  all  that  internal  coloration,  however 
brilliant,  that  can  have  no  relation  to  the  external  w^orld, 
because  hidden  from  view;  such  as  the  red  of  blood,  the  yel- 
low of  fat,  the  iridescent  tints  of  the  swam-bladder  of  fishes, 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     423 

and  opalescent  tints  of  the  inner  surface  of  molluscan  shells. 
We  pass  also  that  coloration  of  purely  physiological  value, 
even  though  it  be  adaptive,  such  as  the  black  color  of 
hibernating  arctic  insects,  adapted  to  absorbing  the  maxi- 
mum amount  of  heat  during  the  short  summer  season ;  and 
the  white  color  of  winter  animals  of  the  same  region,  secur- 
ing them  against  the  too  great  loss  of  their  own  animal  heat 
supply  through  radiation.  We  study  that  adjust- 
ment of  color  and  form  that  has  to  do  with  being 
seen,  that  doubtless  did  not  exist  in  the  beginning,  that 
came  into  existence  when  animals  began  to  hunt  with  their 
eyes;  that  has  been  developed  along  with  the  perfecting  of 
organs  of  vision. 

There  are  some  coloration  phenomena  so  very  common 
and  widely  distributed  that  they  may  be  studied  in  abun- 
dant examples  anywhere.  These  are  resemblance,  flash 
colors,  warning  coloration,  and  mimicry. 

Resemblance. — Few  animals  can  afford  to  be  conspicuous 
— only  those  possessed  of  sufficient  swiftness  or  agility  to 
escape  their  ordinary  enemies,  or  those  possessing  special 
means  of  defense.  For  most  animals,  to  be  conspicuous  is 
to  invite  destruction.  Hence  the  majority  of  animals, 
although  conspicuous  enough  when  exhibited  in  museums, 
are  in  their  proper  environment  to  be  found  only  by  careful 
searching. 

Natural  selection  furnishes  a  simple  and  satisfactory 
explanation  of  resemblance.  The  less  fitly  colored,  being 
the  more  conspicuous,  are  the  ones  eliminated  by  enemies, 
leaving  those  that  are  better  concealed  by  their  coloration  to 
survive  and  perpetuate  in  their  descendants  their  own 
inconspicuousness. 

The  most  general  and  fundamental  phenomenon  of 
resemblance  is  the  darker  pigmentation  of  the  side  of  the 
body  that  is  uppermost  and  the  shading  off  lighter  below,  to 


424  GENERAL  BIOLOGY 

counteract  the  body's  own  shadow.  This  is  well  nigh  uni- 
versal. That  it  is  of  primary  importance  in  bringing  about 
inconspicuousness  any  one  may  demonstrate  by  placing  two 
skins  of  any  common  gray  bird  or  mammal  on  the  bare 
ground,  one  back  upward  in  its  normal  position,  and  the 
other  back  downward,  and  then  looking  at  them  from  a  little 
distance.  The  conspicuousness  of  the  gray  of  the  body 
when  the  shadow  of  the  body  is  added  to  it  will  be  most 
striking,  and  the  advantage  of  the  lighter  countershading 
will  be  apparent.  And  if  one  look  carefully  at  a  living  or 
well  mounted  specimen  of  a  sandpiper  or  a  wild  gray  rabbit, 
he  will  see  how  delicately  this  shading  and  countershading 
is  wrought;  each  little  projecting  ledge  is  overspread  with 
darker  pigmentation;  and  underneath  is  a  lighter  area,  as 
under  the  orbit,  under  the  ear,  or  under  the  chin. 

That  this  plan  of  ground  coloration  is  adaptive,  is  evi- 
denced by  those  animals  that  move  habitually  in  an  inverted 
position,  as  the  sloth,  that  travels  hanging  by  its  claws 
beneath  the  boughs  of  forest  trees,  and  the  back  swimmer 
that  swims  with  its  back  downward  in  the  pond.  Such 
forms  have  the  counter  shading  of  lighter  color  on  the  back. 

Resemblance  is  .spoken  of  as  protective,  helping  its 
possessor  to  escape  its  enemies,  or  aggressive  allowing  its 
possessor  to  approach  unobserved  nearer  its  prey;  but 
the  difference  is  not  in  the  coloration,  but  in  the  purpose  it 
serves.  This  finds  its  analogy  in  the  devices  to  which  men 
resort.  The  modern  soldier  not  wishing  to  offer  in  himself 
a  good  target,  wears  a  khaki  uniform;  and  the  hunter, 
desiring  to  get  closer  to  his  game,  adopts  outer  clothing  of 
similar  inconspicuous  color.  The  gray  mixed  coloration  of 
the  rabbit  or  the  roadside  grasshopper  or  the  green  of  the 
meadow  grasshopper,  and  that  of  most  herbivorous  animals 
is  protective;  while  the  same  colors  in  the  lynx  and  the 
mantis,   and  in  most  carnivorous  species  are  aggressive. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     42  5 


However,  in  very  many  species,  it  may  be  protective  toward 
a  group  of  stronger  species  (enemies)  and  aggressive  toward 
a  group  of  weaker  ones 

Resemblance  is  very  often  a  matter  of  form  and  attitude, 
quite  as  much  as  of  coloration.  The  moths  shown  in  figure 
247  are  colored  much  like  the  burdock  stem  on  which  they 
rest,  but  their  inconspicuousness  is  obviously  greatly 
improved  by  the  stub-like  attitude  in  which  they  hold  the 
body  against  the  side  of  the  stem.  Inconspicuousness,  may 
be  brought  about  by  loss  of  color.  This  is  seen  in  the  trans- 
parent larva  of  Corethra,  and  in  many  free  swimming 
organisms  which  are  viewed  by  enemies  against  the  lighted 
background  of  the  sky.  , 

It  is  impossible  to 
judge  resemblance 
except  in  its  proper 
setting.  An  animal 
that  appears  con- 
spicuous enough  in 
the  museum  (fig. 
248)  may  be  well 
concealed  in  its 
native  haunts.  Cer- 
tainly the  leopard 
frog  with  its  green 
skin  covered  with 
black  blotches  sur- 
rounded by  yellow 
rings  is  conspicuous 
enough  sitting  on  a 
white  plate  in  the 
laboratory,  but  any 

Fig.  247.  Burdock  moths  (.Ue....r.a  lapella)  on  a  OUC  who  haS  COllcCtcd 
dead  stem:  resemblance  in  form  and  attitude  as  fj^jg  frOC  knOWS  it  iq 
well  as  in  color.  6  >5 


42  6 


GENERAL  BIOLOGY 


Fig.  248.  A  moth  (Endryas  unio)  that  is  a  conspicuous 
museum  specimen,  but  quite  inconspicuous  in  its  proper 
haunts. 

very  hard  to  see  until  it  jumps.  Sitting  amid  the 
mixed  vegetation,  its  blotches  fall  into  places  among  the 
leaves  as  lights  and  shadows,  and  tell  no  tales  of  its 
presence.  The  most  conspicuous  of  cross  bands  and 
bars  may  in  nature  be  fit  adjuncts  of  concealment.  For 
example,  the  white  ring  about  the  neck  of  the  plover, 
serves  outdoors  to  detach  the  head  from  the  body,  and 
thus  to  break  the  outline  of  a  bird  into  two  less  easily 
recognizable  parts. 


Fig.  249.     Tree-frog  (Hyla)  on  gray  bark  of  the  buttonbush. 


ADJUSTMENT  OF  ORGAXISMS  TO  ENVIRONMENT      427 

A  few  animals  have  the  power  to  alter  their  coloration  to 
match  their  environment.  The  common  tree  frog  is  one  such. 
The  specimen  shown  in  figure,  (fig.  249)  was  of  a  perfect 
gray  color  while  it  sat  on  the  button  bush  stem,  and  a  short 
time  after  being  transferred  to  the  leaves,  it  was  equally 
inconspicuous  by  reason  of  its  beautiful  green  color. 


Fig.  250.     A  dragonfly  {JEschna  constricta) . 

Flash  colors. — There  is  a  class  of  conspicuous  markings 
upon  the  bodies  of  animals  that  is  not  for  continuous  exhibi- 
tion, and  concerning  the  function  of  which  the  greatest 
diversity  of  opinion  has  been  held.  Since  these  are  usually 
exposed  intermittently  in  flight,  we  may  use  the  non-com- 
mittal name  of  flash  colors  for  them.      Such  are  the  white 


428 


GENERAL   BIOLOGY 


bars  of  the  wings  of  a  night  hawk,  or  the  golden  shafts  of  the 
flicker,  or  the  white  side  spots  of  a  junco's  tail,  or  the  white 
rump  of  a  rabbit,  exposed  only  when  the  tail  is  lowered  in 
running,  or  the  brilliant  reds  and  blacks  of  the  underwing 
moths,  etc.,  etc.     These  are  suddenly  flashed  into  view  when 


Fig.  251.     A  carrion   beetle   i.\ecrophor us) -.coloxs  dull 
red  and  black. 

their  possessor  takes  flight,  and  as  suddenly  tucked  away 
again  on  ahghting.  They  have  been  called  "recognition 
marks"  on  the  assumption  that  they  enable  a  fleeing  herd  of 
gregarious  animals  of  one  species  to  keep  together  or  help 
individuals  to  find  one  another  more  readily.     But  it  seems 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     429 


in  many  cases  at  least  as  if  they  serve  rather  to  promote  the 
bewilderment  of  a  pursuing  enemy.  For  the  alighting 
place  is  usually  a  little  off  to  one  side  of  the  line  of  flight ; 
the  flight  is  easily  followed;  so  easily,  in  fact,  by  reason  of 
the  flash  colors,  that  when  they  suddenly  disappear  on  the 
alighting  of  their  possessor,  pursuit  is  throwm  off  the  track. 
Anyone  may  convince  himself  of  their  fitness  for  such 
bewildering  function  by  following  a  flock  of  juncos  to  their 
alighting  place  in  the  fence  row. 

Warning  Coloration. — The  few  animals  that  everyone 
sees  moving  or  resting,  are  either  able  like  the  great  dragon- 
fly (fig.  250)  to  escape  their  enemies  by  reason  of  their  speed, 
or  else  are  conspicuous  for  a  purpose — possessed  of  some  bad 
quality ,  making  them  undesirable  for  food,  like  the  crow,  or  of 

some  offensive  odor,  like  the  carrion 
beetle  (fig.  251),  or  of  some  bad  flavor, 
like  the  milkweed  bug  (fig.  252),  or  of 
some  special  defense,  like  the  sting  of 
the  bumble  bee.  It  is  advantageous  to 
such  forms  to  be  conspicuous.  They 
are  easily  recognized  and  are  for  the 
most  part  let  alone.  Unlike  the  rabbit 
w^hich  runs  to  hide,  the  skunk,  secure 
in  the  possession  of  an  intolerably 
malodorous  secretion,  walks  along  in 
the  open,  with  his  great  black  and  white 
tail  lifted  aloft,  like  a  banner  in  the  sky. 
Fig  25^  The  milk  weed  ^^  is  of  advantage  to  the  whole  group  of 
/aL5...):^?oiors?edind  wamingly  colored  animals  that_  their 
^^^^^-       : ,  colors   are    few    and    patterns  simple. 

Their  enemies,  which  do  make  experi- 
ments sometimes  in  youth  w^hile  learning,  and  sometimes 
when  greatly  pressed  by  hunger,  have  fewer  combinations 
to  learn  to  avoid,  and  both  sides  are  saved  unpleasant  experi- 


43° 


GENERAL   BIOLOGY 


menting.  The  combinations  are  (aside  from  black  alone, 
which  is  conspicuous  enough  against  green  foliage  or  against 
the  sky)  black  and  yellow,  black  and  white,  black  and  green, 
and  black  and  red  or  orange,  and  the  patterns  are  broad 
cross  bands  of  alternating  colors,  or  extensive  blotches. 

Eyespots  are  the  most  specialized  of  warning  colors. 
They  are  eye  pictures  (fig.  253),  more  or  less  realistically 
drawn  by  nature  upon  some  part  of  the  body  (usually  remote 
from  the  true  eyes)  of  their  possessor,  and  where  v/ell 
exposed  to  the  view  of  an  enexTiy.  They  are  always  large 
enough  to  belong  to  some  creature  many  times  the  size  of 
the  one  exhibiting  them.  They  thoroughly  frighten  ignor- 
ant people,  and  it  is  highly  probable  that  they  frighten 

such  animals  as  occasionally  come 
upon  them  in  the  open.  Their  effi- 
ciency must  depend  in  part  on  their 
rather  infrequent  occurrence,  for 
familiarity  would  abrogate  alarm. 

Mimicry. — So  well  established  are  the 
general  types  of  coloration  accompany- 
ing disagreeable  qualities,  that  some 
animals,  which  lack  special  defense 
have  taken  them  on.  The  robber  fly 
shown  in  figure  254a  so  closely  resem- 
bles the  bumble  bee,  (figure  2546),  with 
which  it  is  associated  in  nature  that  an 
experienced  collector  may  with  diffi- 
culty distinguish  between  the  two  spe- 
cies while  in  flight.  The  fly  possesses  no 
sting  or  other  special  defense ;  it  doubt- 
less secures  considerable  immunity 
from  molestation  by  reason  of  its  likeness  to  the  well-armed 
bumble  bee.  Most  of  our  commoner  mimickers,  have  taken 
on  more  or  less  of  the  coloration,  form  and  attitudes  of  the 


Fig.    253.     The  owl  beetle 
(  \laus  oculatus). 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     431 

Stinging  hymenoptera,  bees  and  wasps ;  a  few  have  mimicked 
ants  which  are  distasteful  by  reason  of  the  formic  acid  they 
secrete;  a  few  have  mimicked  unpalatable  species  in  other 
groups,  the  best  known  of  which  is  probably  the  viceroy 
butterfly  which  mixnicks  the  monarch.  There  are  some 
examples  of  coloration  phenomena  so  fit,  so  admirable  in 
f>very  specific  detail,  of  color  form  and  posture,  and  so  well 


Fig.  254.      Mimicry,     a,  a   robber   fly  {Dasyllis  grossa) 
which  mimicks  the  bumblebee  b  {Bombus). 

adapted  to  the  purpose  they  seem  to  serve  in  nature,  that 
they  excite  our  instant  admiration.  But  of  the  animals  one 
may  gather  in  an  hour's  collecting,  many  will  show  less  fit- 
ness, and  some  will  have  a  coloration  that  appears  to  be 
without  adaptive  significance.  Coloration  existed  before  it 
became  adaptive.  There  is  danger  of  finding  here,  as  in  the 
case  of  the  coloration  of  flowers  (Chap,  i)  adaptive  signifi- 


432  GENERAL   BIOLOGY 

cance,  where  only  structural  and  physiological  colors  are 
present.  Such  furnished  the  materials  out  of  which  adapta- 
tion could  proceed  by  natural  selection.  Feathers,  for 
example,  were  structurally  adaptable  to  longitudinal  streak- 
ing,and  birds  have  furnished  most  of  those  streaked  patterns 
among  animals  that  fit  into  a  grassy  environment.  The 
family  Syrphidae  of  Diptera,  which  has  furnished  our  most 
numerous  examples  of  mimicry  of  the  stinging  hymenop- 
tera  was  doubtless  predisposed  toward  the  colors  and  forms 
of  that  family  from  the  beginning ;  likeivise  the  crane  flies 
that  imitate  grass  spiders.  Doubtless  the  discerning  powers 
of  the  predatory  species  have  improved  with  the  disguises 
of  their  prey.  It  would  be  too  much  to  expect  in  the  nature 
of  the  case  that  the  devices  always  work,  and  when  we 
examine  a  series  of  any  adaptive  forms,  we  find  such  varying 
degrees  of  excellence  as  indicate  that  the  fitting  process 
is  still  in  progress. 

Study  5p.     Examples  from  the  local  fauna  of  the  principal 

types  of  animal  coloration. 

Apparatus  needed. — Individual  insect  nets  and  cyanide 
bottles,  note  books  and  pencils;  if  coloration  of  birds  is  to 
be  specially  observed,  opera  glasses  will  be  of  assistance. 

The  most  abundant  supply  of  material  wdll  be  obtained 
by  "sweeping"  the  grass  with  the  insect  net,  for  protectively 
colored  forms  and  collecting  from  flowers  for  the  other  two 
groups.  Hand  picking  from  the  trunks  of  trees,  etc.,  will 
also  be  useful. 

The  record. — It  is  essential  that  the  record  called  for 
below  be  made  in  the  field,  each  species  being  studied  in  its 
proper  habitat,  where  alone  the  significance  of  its  coloration 
can  be  seen. 

Include  in  the  tables  a  few  well  selected  examples  and 
omit  doubtful  cases. 


ADJUSTMENT  OF  ORGANISMS  TO  ENVIRONMENT     433 
I.     Ilhistrations  of  resemblance. 


Name      Order  I  Coloration 


Resemblance 


general  or  specific        details 


2.     Illustrations  of  flash  colors. 


Name  [Order  I  Color 


Exposed  to  view 


how  I  when 


Folded  away 
how 


Possible 
use? 


J.     Illustrations  of  warning  coloration. 


Name  i  Order    I  Colors      Pattern 


Disagreeable      quality 
advertised 


4.     Illustrations  of  mimicry. 


Name      Order      Coloration      Mimicks  what 


whose 
defence  is 
what? 


CHAPTER   VII. 


THE  RESPONSIVE  LIFE  OF  ORGANISMS. 

It  is  a  long  vista  the  science  of  biology  opens  to  our 
imagination.  At  the  farther  end  is  formless  protoplasm, 
moving  with  the  first  thrill  of  responsive  adaptiveness  to 
the  external  world.  Along  the  way  are  ranged  all  the 
form-changes  and  all  the  acquired  powers  of  organic  life. 
At  this  end  is  the  wonderful  assemblage  of  living  forms; 
among  them,  the  human  organism,  with  a  mind  that  con- 
templates all,  and  endeavors  to  understand — all,  and  withal, 
itself. 

Mind  in  man  is  made  known  in  speech 
and  action;  the  psychic  life  of  animals, 
in  actions  alone.  If  the  acts  of  animals 
are  like  those  we  perform  under  similar 
circumstances,  we  are  inclined  to  infer 
that  animals  possess  kindred  psychic 
states.  Thus,  from  their  behavior,  we 
think  we  recognize  hunger  and  satiety, 
anger  and  fear,  pain  and  pleasure,  in 
the  expressions  of  animals,  and,  in- 
FiG.  255.  Melancholy,  deed,  somc  of  the  Icss  instinctivc  feel- 
ings, such  as  curiosity  in  monkeys  and 
The  great  difficulty  in  interpreting 
psychic  states  in  beings  other  than  ourselves  lies,  of  course, 
in  the  fact  that  the  mind  is  directly  accessible  only  to  its 
possessor.  One  may  not  know  the  mind  of  another  being 
except  by  inference.  Great  difficulties  attend  the  inter- 
pretation of  the  psychic  states  of  even  those  animals  that 
are  most  like  us  in  bodily  organization,  and  the  difficulties 
become  insuperable  in  the  case  of  animals  that  lack  our 


jealousy    in    dogs. 


RESPONSIVE  LIFE  OF  ORGAXISMS  435 

modes  of  expression  *  How  we  should  express  any  emotion 
if  we  had  to  do  it  with  a  hydroid's  tentacles,  we  cannot 
conceive. 

Nevertheless,  there  is  no  living  thing  that  lacks  the 
power  of  making  visible  response  to  the  conditions  of  the 
external  world — such  response  as  no  inorganic  thing  ever 
manifests.  This  response  may  be  slow,  as  in  most  plants, 
or  rapid,  as  in  most  animals  possessed  of  parts  having 
specialized  contractility;  but  it  is  always  in  evidence,  and 
in  the  last  analysis  it  is  the  most  distinctive  characteristic  of 
life.  Even  growth  and  reproduction  are  but  manifestations 
of  it. 

The  capacity  for  responding  to  stimuli  is,  as  we  have 
already  seen,  a  property  of  protoplasm.  When  we  watch 
the  streaming  of  protoplasm  in  a  plant  cell  we  may  see  it 
accelerated  or  retarded  with  every  change  of  temperature. 
A  little  slime-mold  Plasmodium  placed  in  a  half  lighted  posi- 
tion will  move  away  from  the  light  and  into  the  shadow.  It 
will  creep  toward  a  decoction  of  dead  leaves  (its  proper 
food),  and  away  from  a  solution  of  quinine.  Such  a  bit  of 
naked  protoplasm,  therefore,  although  quite  destitute  of 
organs,  moves  freely,  and  in  a  fundamental  and  important 
sense  it  both  perceives  and  acts. 

The  behavior  of  organisms,  which  is  the  visible  manifesta- 
tion of  their  psychic  life,  shall  be  the  subject  of  our  study  in 


*"A  bodily  structure  entirely  unlike  our  own  must  create  a 
background  of  organic  sensation  which  renders  the  wh()lc  mental 
life  of  an  animal  foreign  and  unfamiliar  to  us.  We  s])eak,  for 
example,  of  an  angry  wasp.  Anger  in  our  own  experience  is 
largely  composed  of  sensations  of  quickened  heart-beat,  of  altered 
breathing,  of  muscular  tension,  and  of  increased  bl()()d-])ressure  in 
the  head  and  face.  The  circulation  of  a  wasp  is  fundamentally 
different  from  that  of  a  vertebrate.  A  wasp  does  not  breath 
through  lungs,  it  wears  its  skeleton  on  the  outside,  and  it  has 
muscles  attached  to  the  inside  of  the  skeleton.  What  is  anger 
like  in  the  wasp's  consciousness?     We  can   fonn  no  adequate  idea 

of  it." 

— \l  ashburn. 


43^ 


GENERAL  BIOLOGY 


this  chapter.  Behavior  is  our  only  clue.  By  behavior  we 
judge  whether  a  thing  is  alive  or  not.  Responses  alone  can 
show  us  whether  there  is  anything  within  an  organism 
capable  of  taking  cognizance  of  external  conditions.  And 
responses  show,  also,  which  of  the  conditions  of  the  external 
world  an  organism  perceives.  Psychic  phenomena  are 
essentially  subjective,  and  our  knowledge  of  them  consists 
(except  in  ourselves  alone)  in  inferences  based  on  their 
corresponding  objective  manifestations.  The  primary  rela- 
tions existing  between  the  subjective  and  the  objective,  may 
be  graphically  stated  thus : 


Objective 
phenomena 

Subjective 
phenomena 

Stimulus  ^ 

Sensation 

» 

Act 

,^^J     Impulse 

This  is  merely  a  graphic  statement  of  the  evident  facts 
that  environment  (external  or  internal)  gives  the  stimulus, 
which  upon  the  psychic  side,  produces  the  sensation  (feeling, 
taste,  sight,  etc.),  which  may  be  accompanied  by  an  impulse 
(also  subjective),  and  may  eventuate  in  an  act.  The  act, 
therefore,  is  thus  the  last  link  in  a  chain  of  events :  the  effect 
of  a  succession  of  causes.  However  diverse  the  structure  of 
organisms,  their  parts  that  are  most  directly  subservient  to 
the  psychic  life  are  of  two  sorts : 

i)  Receptive  organs,  capable  of  being  influenced  by 
stimuli.  These  are  the  parts  through  which  the  external 
world  makes  its  impressions  upon  the  sensory  mechanism. 

2)  Active  or  motor  organs,  capable  of  making  appropriate 
rodsanses.  These  are  the  parts  through  the  agency  of  which 
the  psychic  states  are  made  manifest. 


RESPOXSIVE  LIFE  OF  ORGANISMS  437 

I.     Animal  Activities. 

I.      Some  typical  sensory  phenomena  of  the  Protozoa. 

In  such  an  organism  as  an  amoeba,  which  lacks  as  we  have 
seen,  permanent  organs  of  either  of  the  classes  just  men- 
tioned, we  may  observe  activities  of  the  same  sorts  as  those 
above  cited  for  the  slime-mold  Plasmodium.  An  amoeVja 
creeps  about  freely,  manifesting  like  movements  of  contact 
and  avoidance.  It  adjusts  the  form  of  its  body  to  getting 
through  narrow  passageways,  it  changes  its  course  of  loco- 
motion in  avoidance  of  an  obstruction.  Now  and  then  it 
makes  a  more  special  response  to  things  in  its  environment. 
Coming  in  contact  with  a  diatom,  or  other  small  organism 
suitable  for  food,  the  amoeba  moves  toward  it,  extends  its 
pseudopodia   and   flows   about   it,    and   finally   completely 

engulfs  it.  This  is  a  definite  food 
taking  reaction.  On  the  other  hand, 
it  withdraws  itself  promptly  from  a 
sharp  mechanical  stimulus,  such  as 
the  prick  of  a  glass  stylus  (fig.  256), 
a  wave  of  movement  in  the  proto- 
plasm of  its  body  away  from  the 
point  stimulated,  being  immediately 
discernible. 

''ieoidfnl-reaSnlnAmoeb'a^         To     what     SOrt     of     psychic     StateS 

fateV^by^T g?a"rsfyius'"' b'  "t^ese  simplc  cxtcmal  acts  may  corre- 
SLXSnorSLwo/^heSpond  wc  cauuot  say.  What  the 
protoplasm.      (After     Jen-  ^^orld  and  the  things  therein  may  be 

like  to  an  animal  of  this  sort  we  could 
only  know  by  being  amoebas  awhile.  Indeed,  we  cannot 
conceive  what  it  would  be  like  to  ourselves  if  we  had  never 
seen  or  handled  things,  and  if  we  had  no  means  of  knowing 
objects  as  such,  but  only  as  the  obtruding  parts  of  a  general 
environment.     Perhaps,  there  may  be  some  sort  of  vague 


438  GEXERAL  BIOLOGY 

agreeableness  or  disagreeableness,  some  sort  of  organic 
sense  of  comfort  or  of  discomfort,  connected  with  and 
occasioning  the  reactions  of  the  two  sorts. 

Organs  of  out-reach. — Impermanent  pseudopodia  are  the 
amoeba's  only  means  of  exploring  its  environment,  but  the 
higher  protozoans  possess  cilia  and  flagella.  These  are 
permanent  organs  of  out-reach,  in  which  sensory  and  motor 
functions  are  combined.  These  enable  their  possessor  to 
reach  out  and  touch  an  object  before  coming  into  bodily 
contact  with  it.  These  give  time  and  opportunity  for 
avoidance  of  collisions  and  for  escape  from  approaching 
enemies.  Indeed,  if,  with  specialized  sensibility,  these  be 
capable  of  receiving  vibrations,  they  may  give  warning  of 
the  proximity  of  an  enemy  before  coming  into  actual  con- 
tact with  it.  These  make  the  course  of  an  animal  through 
the  water  less  groping  in  proportion  to  their  length  or 
sensitiveness.  It  is  the  method  of  a  blind  man  exploring 
his  pathway  with  his  cane.  The  long  fiagellum  which 
Euglena  (fig.  6i  on  p.  105),  swings  before  it  as  it  swims, 
explores  a  relatively  wide  pathway. 

But  Euglena  has  also  an  "eye  spot"  at  the  forward  end  of 
the  body,  and  is  capable  at  least  of  discerning  between  light 
and  darkness;  and  therefore,  if  compared  with  a  blind  man, 
the  comparison  should  be  with  one  whose  blindness  is  not 
total.  Euglena  swims,  as  we  have  seen,  habitually  into  the 
better  lighted  areas  of  its  watery  environment.  In  doing 
this  it  must  be  guided  not  so  much  by  its  tactile  sense, 
(which  is  more  directly  concerned  with  the  objects  of  its 
immediate  environment),  as  by  vibrations  of  light  coming 
from  a  greater  distance.  Here,  then,  is  the  beginning  of 
another  kind  of  perceptive  organ — one  whose  efficiency 
depends,  not  on  the  out-reach  of  a  sensitive  part  of  the 
body,  but  on  specialized  sensibility  of  a  part  to  the  inflow 
of  vibratory  stimuli  coming  from  a  distance.     The  range  of 


RESPONSIVE   LIFE  OF   ORGAXISMS 


439 


perception  is  by  such  an  organ  enormously  increased.  This 
fleck  of  pigment  in  Euglena  is  the  rudiment  of  an  organ,  pos- 
sessing increased  sensibility  to  light;  and  it  is  doubtless  no 
more  an  accident  that  it  should  lie  in  the  front  end  of  the 
body,  than  that  a  vertebrate's  eyes  should  be  located  in  its 
head. 

Some  reactions  of  Paramoecium. — Improvements  in  the 
organization  of  the  body  of  Paramoecium  are  by  no  means 
confined  to  the  development  of  cilia.  These  are  but 
specialized  parts  of  the  ectoplasm,  which  depend  largely  for 
their  efficiency  on  further  differentiation  of  other  parts  of 
it.  The  general  outer  surface  of  the  ectoplasm  has  become 
thickened,  giving  permanence  of  form  to  the  body  and 
solidity  of  support  for  the  cilia.     In  the  underlying  ecto- 


pic 257.  Diagrams  of  behavior  in  Paramoecium.  a,  the  avoiding  reaction;  /  to  6 
successive  positions:  arrows  indicate  directions  of  movement,  b  the  contact 
reaction.      (After  Jennings) 

plasm  are  developed  strands  of  substance  for  sensory  com- 
munication between  various  parts  of  the  cell  body;  and 
these  doubtless  enable  the  cilia  to  act  in  unison,  to  stop  or 
start  or  reverse  their  movements  with  promptness  and 
efficiency.  Therefore,  the  speed  and  precision  of  its  loco- 
motions and  the  promptness  and  extent  of  its  responses  to 
stimulation  are  vastly  better  than  in  amoeba. 


440  GENERAL  BIOLOGY 

The  specialized  activities  of  Paramoecium  have  made  of  it 
a  good  deal  of  an  automaton.  Aside  from  the  ordinary 
swimming,  in  a  spiral  course,  with  the  oral  groove  toward 
the  axis  of  the  spiral  (see  page  73),  it  has  one  reaction  that 
is  prominent  above  all  others — a  definite  avoiding  reaction. 
Meeting  with  almost  any  sort  of  stimulus  it  stops,  ceases 
rotation,  swims  backward  a  little  way,  turns  a  little  to  the 
aboral  side,  and  then  starts  swimming  forward  again  (fig. 
257a).  If  the  change  of  direction  were  not  sufficient  to 
clear  the  obstruction  (or  other  source  of  stimulus),  the 
reaction  is  repeated;  and  it  continues  to  be  repeated  in  a 
perfectly  automatic  manner  until  the  course  is  again  clear. 

Food-taking  in  paramoecium  appears,  as  we  have  seen 
(page  75),  to  be  an  equally  automatic  and  undiscriminating 
performance,  digestible  and  indigestible  substances  being 
taken  into  the  body  with  equal  readmess. 

There  is  also  a  contact  reaction  observable  in  Paramoe- 
cium. When,  in  swimming  about,  one  comes  into  gentle 
contact  with  a  bit  of  soft  vegetable  substance,  it  may  come 
to  rest  in  the  manner  shown  in  figure  257Z),  with  a  number  of 
its  cilia  extended  in  direct  contact  with  the  object.  Thus, 
it  may  remain  quietly,  as  if  at  a  satisfactory  anchorage,  for  a 
considerable  time.  Doubtless  it  is  in  the  neighborhood  of 
such  soft  substances  that  its  proper  food  is  likely  to  be  found. 
And  when  a  paramoecium  is  thus  resting  it  is  less  responsive 
than  at  other  times  to  ordinary  stimuli.  For  example,  a 
slight  mechanical  stimulus,  such  as  a  light  touch  on  the  tips 
of  its  cilia,  may  pass  unnoticed,  whereas  the  same  stimulus 
if  applied  to  one  not  thus  situated  would  instantly  call  forth 
the  avoiding  reaction. 

In  all  the  Protozoa  there  are  certain  activities  (and  cessa- 
tions of  activity,  equally  significant)  that  indicate  that  the 
actuating  stimuli  are  of  internal  origin.  Apparent  spon- 
taneity of  movement  may  be  due  to  external  influences  that 


RESPONSIVE  LIFE  OF  ORGANISMS  441 

escape  our  observation;  but  the  constant  differences  of 
behavior  of  a  single  organism  when  hungry  and  when  well 
fed  must  be  due  to  stimuli  arising  out  of  its  bodily  states. 
When  well  fed,  it  is  less  active  and  always  less  responsive  to 
external  stimuli  of  every  sort.  A  far  more  striking  examjjle 
is  offered  by  the  cyclic  conjugating  reaction  of  Paramoccium 
(see  page  iii),  which  occurs  at  long  intervals.  Two  com- 
plemental  individuals  come  together  for  exchange  of 
nuclear  substances.  These  cycles  suggest  the  breeding 
periods  of  the  higher  animals,  during  which  the  maturing  of 
the  sex  cells  occasions  internal  stimuli  which  call  forth  a 
whole  train  of  activities  that  are  collectively  known  as 
"breeding  habits." 

So  the  protozoa,  although  their  acts  are  few  in  kind  and 
simple  in  performance,  exhibit  a  set  of  elemental  reactions 
of  the  most  fundamental,  wide  spread,  and  comprehensive 
sort. 

2.     Some  general  features  of  the  sensory  inechauis)}i  of 

the  Metazoa. 

Protozoan  and  metazoan  are  alike  organic  wholes.  Each 
has  developed  about  itself  a  protecting  outer  wall,  sequester- 
ing itself  from  the  outer  world.  Each  has  created  an  inter- 
nal world,  within  which  all  its  vital  processes  are 
carried  on  through  the  concordant  action  of  part  upon  part. 

Whatever  organs  a  protozoan  may  develop,  it  is  limited 
in  this;  that  they  must  all  be  developed  out  of  the  parts  of  a 
single  cell.  In  the  metazoans,  on  the  contrary,  there  are 
many  more  or  less  independent,  structural  units,  that  can  be 
differentiated  for  separate  functions.  One  set  of  cells  ma}^ 
be  made  to  serve  as  receptors  for  stimuli  (end  organs) ; 
another  may  be  specialized  for  doing  the  contracting  (muscle 
fibers),  and  another  (nerve  cells  and  their  processes  or 
fibers),  may  be  fitted  for  intercommunicating  between  the 


442  GENERAL  BIOLOGY 

two  sorts  first  named.  The  feeble  beginnings  of  this 
differentiation  we  have  noted  in  the  hydra  (yage  i6i),  and 
further  development  has  been  briefly  traced  in  the  earth- 
worm (especially  in  the  nerve  cells,  figure  109),  and  in  the 
salamander. 

The  cells  of  a  metazoan  make  common  cause  of  their  rela- 
tion to  the  outside  world,  and,  with  more  materials  out  of 
which  to  build,  greater  progress  in  differentiation  is  made. 
Systems  of  organs  arise;  digestive,  circulatory,  respiratory 
and  excretory  systems  for  performing  the  nutritive  pro- 
cesses of  the  body,  and  nervous  and  muscular  systems,  for 
the  control  and  coordination  of  all,  and  for  maintaining 
proper  relations  with  the  outside  world. 

Intercommunication  without  nerves. — Our  studies  shall 
be  of  this  specialized  apparatus;  but  we  will  do  well  to 
remember  that  receptivity  and  action  are  older  than  nerve 
and  muscle.  These  functions  are  too  general  and  too 
important  to  be  wholly  committed,  even  in  the  highest 
animals,  to  any  particular  set  of  cells.  It  is  the  more 
specialized  activities  that  are  taken  over  by  these  cells,  but 
there  remain  other  important  functions  of  relation  that  are 
yet  fulfilled  by  slower  processes  in  which  nerve  and  muscle 
take  small  part.  Manifestly,  before  nerve  and  muscle  were 
developed  interaction  had  to  be  brought  about  by  contact 
of  adjacent  cells,  as  is  still  necessary  during  early  embryonic 
development.  The  movement  of  a  stimulus  passing  from 
cell  to  cell  was  like  that  of  particle  upon  particle  in  the  body 
of  a  pricked  amoeba  (fig.  256) .  It  is  like  the  slow  communi- 
cation by  word  of  mouth  from  door-yard  to  door-yard,  as 
compared  with  the  telegraphic  communication  of  news. 
When  nerves  develop  they  take  on  wholly  the  function 
of  rapid  communication  between  distant  parts ;  but  certain 
of  the  other  older  and  slower  processes  of  the  bodily  economy 
continue  to  be  performed  by  older  and  slower  methods. 


RESPONSIVE  LIFE  OF  ORGAXISMS  443 

Cell  still  acts  upon  its  neighboring  cell  directly;  and  it  also 
acts  on  all  the  cells  of  the  body  by  contributing  certain  of 
its  products  to  the  fluids  that  bathe  the  whole  interior. 
Many  organs  are  known  to  ]3roduce  internal  secretions, 
which  are  circulated  about  with  the  blood,  and  which  pro- 
foundly affect  the  well-being  of  other  organs.  Thus,  the 
small  intestine  in  vertebrates,  when  stimulated  by  contact  of 
the  acidulated  food  entering  it  from  the  stomach,  produces 
a  substance  (known  as  secretin),  which,  when  carried  by 
the  blood  to  the  pancreas,  incites  that  organ  to  secrete  and 
discharge  its  own  digestive  fluid  (pancreatic  juice).  And 
certain  organs,  like  the  thyroid  gland  (which  in  us  envelope 
the  base  of  the  trachea  on  the  ventral  side,  and  which  is  the 
seat  of  the  disease  known  as  goiter),  have  been  found  to  be 
of  great  importance  by  reason  of  the  internal  secretions 
(hormones)  which  they  contribute  to  the  body  fluids.  If 
for  example,  the  thyroid  gland  be  removed,  its  loss  causes 
both  internal  and  external  derangement.  The  skin  thick- 
ens and  becomes  wrinkled,  the  hair  falls  out,  the  nervous 
balance  is  disturbed,  and  finally,  death  results.  But  if  the 
extract  from  the  thyroid  gland  of  another  animal  of  the 
same  species  be  injected  periodically  underneath  the  skin, 
these  results  will  not  follow  the  removal  of  the  gland. 
Similarly,  the  sex  organs  appear  to  produce  hormones  that 
condition  the  development  of  secondary  sexual  characters. 
For  when  the  spermary  of  a  young  cockerel  is  removed,  comb 
and  spurs  and  the  other  external  signs  of  his  sex  are  checked 
in  their  development;  but  they  can  be  made  to  develop  by 
merely  grafting  into  his  body  a  piece  of  the  spermary  of 
another  cockerel.  So,  it  appears  probable  that  to  this  fluid 
which  bathes  all  the  tissues  of  the  body  and  conditions  its 
metabolism,  every  cell  may  contribute  something,  and  the 
general  condition  of  the  body  may  be  largely  determined  by 
the  totality  of  this  contribution.     Internal  secretions  or 


444  GENERAL  BIOLOGY 

hormones,  therefore,  appear  to  be  an  important  part  of  the 
self-regulating  mechanism. 

Sense  organs. — The  exigencies  of  animal  existence 
demand  that  the  functions  of  relation  to  the  outside  world 
should  be  performed  as  speedily  as  possible — that  stimuli 
should  be  quickly  received  and  transmitted  and  translated 
into  useful  acts. 

Now  the  stimuli  are  of  various  sorts.  Some,  like  the  pull 
of  gravity  or  the  change  of  temperature  act  constantly  or 
slowly,  and  there  may  be  no  special  sense  organs  for  their 
reception.  Others  of  mechanical,  chemical  and  vibratory 
nature  have  caused  the  development  of  sense  organs  of  the 
most  specialized  sorts. 

1.  Mechanical  stimuli  produce  the  sensation  of  touch. 
Special  receptors  for  mechanical  stimuli  are  scattered  about 
over  the  bodies  of  all  the  higher  animals.  They  abound 
in  the  tips  of  outgrowing  organs  that  are  specially  exposed 
to  contact  with  external  objects.  The  earlike-lobes  at  the 
front  end  of  a  planarian,  and  the  prostomium  of  an  earth- 
worm are  very  sensitive  to  touch.  In  our  own  skin  tactile 
organs  are  least  numerous  in  the  middle  of  our  backs  and 
most  abundant  in  the  tips  of  fingers  and  tongue. 

2.  Chemical  stimuli  give  rise  to  sensations  of  taste  and 
smell.  Some  sort  of  discernment  of  the  difference  between 
edible  and  inedible  substances  is  well-nigh  universal  among 
animals.  Since  food  is  limited  in  quantity  and  distribution, 
there  is  need  that  it  should  be  recognized.  In  an  aquatic 
organism  doubtless  these  two  classes  of  sensation  are  not  very 
different  in  kind ;  indeed  they  are  not  always  sharply  distin- 
guished in  ourselves.  One  may  bite  of  an  onion  and  not  be 
very  sure  whether  his  impression  of  the  thing  is  mainly  of 
its  taste  or  its  smell.  Volatile  particles  may  travel  through 
the  air  and  so  may  reach  the  olfactory  organ  from  a  distance. 
Hence  the  sense  of  smell  is  less  exclusively  subservient  to  food 


RESPONSIVE  LIFE  OF  ORGANISMS  445 

selection,  and  may  be  made  to  serve  other  perceptive  func- 
tions, such  as  the  locating  of  enemies  or  the  recognition  of 
friends  and  kindred  in  terrestrial  animals.  Dogs,  and  many- 
wild  vertebrates,  depend  upon  this  sense  apparently  for  a 
very  large  part  of  the  knowledge  of  the  world  they  live  in. 

The  sense  of  smell  in  the  human  species  is  not  at  its  best 
development.  Anyone  may  convince  himself  of  this  by 
the  most  casual  observation  of  the  actions  of  his  own  dog. 
We  cannot  know,  of  course,  what  smells  are  like  to  a  dog, 
any  more  than  we  may  know  of  any  other  sense  impression 
of  which  we  have  had  no  experience;  but  we  cannot  doubt 
that  they  are  to  him  a  means  of  fine  discrimination. 

Since  chemical  substances  must  be  in  solution,  or  in 
gaseous  form,  in  order  that  they  may  affect  the  organs  of 
taste  and  smell,  the  receptors  of  these  organs  in  terrestrial 
animals  are  withdrawn  into  moistened  cavities  within  the 
body,  where  they  are  protected  from  evaporation. 

Since  the  animal  body  is  a  sort  of  chemical  engine,  it  is 
not  strange  that  chemical  stimuli  are  frequently  the  actuat- 
ing causes  that  call  forth  various  responses  within  the  body. 
It  is  by  means  of  chemical  reactions  set  a-going  within  the 
retina  of  the  eye,  that  the  weak  stimuli  of  light  vibrations 
are  reinforced  and  made  effective  in  proportion  to  their 
importance. 

3.  Rays  of  light  produce  the  sensation  of  vision.  At  its 
beginning,  vision  is  nothing  more,  perhaps,  than  a  dim 
awareness  of  a  difference  existing  between  light  and  dark- 
ness. The  eye  doubtless  has  had  a  long  line  of  antecedents. 
It  may  have  begun  as  a  red  "eye  spot"  like  that  of  Euglena, 
and  may  have  owed  its  earliest  efficiency  as  a  receptor  of 
vibrations  to  the  greater  absorbing  power  for  radiant  energy 
of  the  lower  colors  of  the  spectrum.  And  it  may  have  been 
responsive  to  heat  rays  rather  than  to  light  rays  at  first. 


446  ,  GENERAL  BIOLOGY 

Ability  to  distinguish  light  from  darkness  might  help  an 
organism  to  adjust  itself  in  position,  but  much  more  than 
this  is  necessary  in  order  that  it  should  really  see  anything. 
In  order  that  a  picture  of  an  external  object  should  be  formed 
in  the  mind,  it  must  first  be  pictorially  impressed  on  multi- 
ple receptors,  so  situated  that  the  rays  of  light  coming  from 
different  parts  of  an  object  may  be  spatially  arranged  there- 
on. Seeing  requires  eyes.  There  is  no  one  of  the  powers 
of  animals  in  which  they  differ  more  profoundly  than  in 
their  capacity  for  light  perception.  Eyes  are  of  the  most 
diverse  structural  types,  and  in  each  of  the  main  types  there 
exist  all  degrees  of  perfection.  The  camera-like  eye  of 
vertebrates,  with  its  inverted  retinal  picture,  differs  funda- 
mentally from  the  compound  eye  of  an  arthropod,  with  its 
mosaic  pattern  and  its  fine  adaptation  for  the  perception  of 
movement.  The  development  of  the  vertebrate  eye  is  one 
of  the  most  fascinating  chapters  in  biology,  but  far  too  long 
a  story  to  be  recounted  here.  Whatever  its  structure,  the 
eye  consists  essentially  of  multiple  receptors  combined  into 
a  single  organ,  and  sheltered  behind  a  transparent  protec- 
tive covering,  the  whole  occupying  an  exposed  position  at 
the  forward  end  of  the  body  and  in  direct  communication 
with  the  more  important  nerve  centers. 

Taste,  smell  and  hearing  give  us  of  themselves  hardly  any 
conception  of  form  or  of  magnitude;  nor  does  touch,  for 
large  objects,  except  in  successive  impressions  as  parts  are 
successively  explored.  But  the  eye  may  instantly  reveal 
the  whole  content  of  environment,  in  form,  in  magnitude,  in 
proportions  and  in  action.  Such  are  the  precious  powers  of 
this  incomparable  organ ;  and  so  great  are  the  advantages  it 
confers  on  its  possessor  that  eyeless  animals  (save  when  so 
small  as  to  be  beyond  the  range  of  ordinary  vision)  are  prac- 
tically absent  from  the  lighted  places  of  the  earth. 

4.  Vibrations  of  air  or  of  solids  produce  the  sensation  of 
sound.     They   also,    under   certain   conditions,    produce   a 


RESPONSIVE   LIFE  OF  ORGANISMS  447 

mechanical  effect  when  they  fall  upon  a  sensitive  surface. 
And  doubtless  tones  are  perceived  as  such  only  by  special- 
ized organs  of  hearing.  Sound  receptors  are  variously 
located  about  the  body,  and  are  wonderfully  different  in 
structure  in  different  groups  of  animals.  The  antennal  hairs 
of  a  male  midge  that  vibrate  to  sound  waves  of  a  length 
corresponding  to  the  pitch  of  the  humming  of  the  female, 
are  freely  exposed.  But  sound  receptors  are  more  often 
sequestered  in  some  part  of  the  body  behind  a  mechanism 
(such  as  the  tympanum  and  small  bones  of  the  middle  ear  in 
ourselves)  capable  of  taking  up  vibrations  and  passing  them 
on  to  appropriate  nerve  endings.  Since  sound  waves  tend 
to  fill  all  the  space  they  traverse,  there  is  not  the  same  need 
as  in  the  case  of  eyes,  that  ears  should  be  located  in  a  well 
exposed  part  of  the  body.  Hence,  we  find  the  sound  recep- 
tors of  certain  grasshoppers  located  in  the  fore  legs,  and  in 
others,  upon  the  base  of  the  abdomen.  These  are  so 
different,  however,  from  the  ears  of  vertebrates,  that  we  can 
form  hardly  any  conception  of  how  they  work,  nor  any  at  all 
of  the  sort  of  sensations  to  which  they  may  give  rise.  The 
ears  of  vertebrates,  situated  on  the  head,  are  placed  in  the 
direct  path  of  passing  sound  waves,  and  trumpet-like  exter- 
nal ears  are  added  for  concentrating  these  waves  upon  the 
eardrum. 

Ears  possess  the  great  advantage  of  giving  notice  of  the 
presence  of  friends  or  enemies  in  the  darkness  as  well  as  in 
the  light,  and  when  hidden  as  well  as  when  in  the  open. 
Well  developed,  they  confer  great  powers  of  discrimination 
upon  their  possessor.  For  social  organisms  ears  have  their 
value  wonderfully  enhanced  by  the  development  of  sound- 
producing  organs.  Together,  these  constitute  the  funda- 
mental equipment  for  social  intercourse,  and  for  exchange  of 
ideas.  Eye  and  ear  are  in  ourselves  the  receptors  to  which 
we  have  learned  as  social  organisms  to  make  appeal. 


448  GENERAL  BIOLOGY 

Nerve  and  muscle.  Pseudopodia,  cilia  and  other  organs 
of  outreach  in  the  protozoa  fulfill  both  sensory  and  motor 
functions.  Separate  classes  of  organs  for  these  functions 
are  not  differentiated;  and  probably  they  were  not  differ- 
entiated at  first  in  the  metazoa.  Nerves  and  muscles  must 
have  originated  near  the  surface  of  the  body,  for  only  there 
could  they  have  been  in  communication  with  the  outside 
world.  It  is  there  we  find  them  first  in  the  phylogenetic 
series,  underlying  the  ectoderm  in  the  hydra  (fig.  loi,  page 
159).  It  is  from  the  underlying  layers  of  the  ectoderm,  as 
we  have  seen,  that  the  nervous  tissues  arise  in  the  ontogeny 
of  the  vertebrates. 

It  is  the  primary  function  of  the  nerve  cell  to  develop  out 
of  its  own  cytoplasm  such  parts  of  out-reach  as  shall  serve 
for  intercommunication  between  all  of  the  other  tissues  and 
with  each  other.  They  must  be  connected  externally  with 
the  sense  organs  of  the  body  and  internally  with  the  muscles 
to  the  end  that  the  sensing  of  the  things  of  the  external 
world  may  bring  about  prompt  and  appropriate  measures 
for  dealing  with  them.  Muscle  cells  must  therefore  be 
developed  in  connection  with  nerves.  They  are  elongate 
cells  of  special  contractility,  connected  with  whatever  solid 
supports  the  body  may  possess.  They  become  aggregated 
together  and  integrated  into  muscles  of  increasing  strength 
and  size  as  the  skeleton  develops,  giving  them  points  of 
insertion,  and  offering  strength  to  resist  their  pull. 

Ganglia. — The  possession  of  long  organs  of  cell  out-reach 
(fibers)  made  it  possible  that  nerve  cells  should  be  removed 
from  the  surface  where  they  develop,  into  the  interior  of 
the  body,  where  better  protected  from  injury.  The  impor- 
tance of  the  regulatory  function  they  fulfill  made  this  highly 
desirable,  and  intercommunication  between  the  cells 
themselves  was  facilitated  by  the  assembling  of  them  togeth- 
er in  groups.     The  simplest  of  these  we  know  as  ganglia. 


RESPONSIVE   LIFE  OF  ORGANISMS 


449 


Ganglia  are  local  centers,  which  exercise  a  regulatory 
function  within  a  more  or  less  localized  portion  of  the  body. 
Their  number  and  arrangement  differs  according  to  the 
structural  plan  of  the  body  to  which  they  belong.  In 
segmental  animals,  like  the  earthworm,  the  ganglia  are 
arranged  segmentally,  each  ganglion  pair  of  the  ventral 
chain  (nerve  cord),  controlling  primarily  its  own  segment. 
In  all  arthropods,  as  we  have  seen,  they  are  arranged  upon 
the  ventral  side;  in  vertebrates,  upon  the  dorsal  side. 
They  are  arranged  so  differently  in  the  different  animal 
phyla  as  to  indicate  that  they  have  been  brought  together 
on  different  developmental  lines,  in  accordance  with  the 
conditions  offered  by  each  structural  type. 

The  neurone. — Nerve 
cells  by  migration  to  the 
centers,  have  become 
widely  removed  from  the 
receptors  at  the  surface 
of  the  body.  That  there 
are  nerve  fibers  connect- 
ing the  two  together  has 
long  been  known  (the 
comparison  of  the  fibers 
to  telegraphic  lines  being 
a  very  old  and  familiar 
one);  but  that  these 
fibers  ar$  an  integral  part 
of  the  central  cells  is  a 
matter  of  recent  knowl- 
edge, derived  from  the 
T.     ^ro     ^  .  ,   ,   ,  .  study    of    their    develop- 

FiG.  258.      Ontogeny    and  phyloReny  in   neu-  •'  ^ 

rones  of   the  middle   layer  of   the    cerebral  ^lent.       Thc  flbcr  aHsCS  aS 
cortex.      A,  B,  C,  Corresponding  cells  trom 

the     adult    brain    in    frog,    lizard  and   rat    g^^       OUterOWine        prOCCSS 
respectively,      a,   to    e.  successive  stages  ot  ^  , 

development    of  cells  of    the    same  sort    in   fj-Qj-Q     the     CcU     bodv     (fig- 
a  mammal:   the  axone  appears  in  a,  den-  -       ^     o* 

drites    in  b      and    collaterals,       in      d,     2  c; 8)         There   maV   bc    One 

(after    ajal)  0    / '  J 


450  GENERAL  BIOLOGY 

(if  a  bipolar  cell)  or  more  (if  multipolar)  additional  pro- 
cesses arising  from  the  opposite  end  of  the  cell  and  extend- 
ing in  different  directions.  The  cell  with  all  its  processes  is 
called  a  neurone.  The  process  which  becomes  the  fiber  is 
called  the  axone;  if  it  gives  off  branches  within  the  nerve 
center  for  communication  with  other  neurones,  these 
branches  are  called  collaterals.  The  processes  arising  from 
the  other  parts  of  the  cell,  are  typically  shorter  and  much 
branched  and  are  called  dendrites  {dendron,   a  tree). 

Division  of  labor  among  the  neurones  has  resulted  in  the 
development  of  two  complemental  sorts  of  them,  one  sort 
being  afferent  in  function,  and  serving  to  conduct  from  the 
receptors  to  the  centers,  and  the  other  being  efferent,  and 
serving  to  carry  impulses  outward  from  the  center  to  incite 
muscle  or  gland  to  action.  The  dendrites  are  at  the  receiv- 
ing end  of  neurone,  while  nerve  impulses  are  carried  outward 
from  the  cell  body  by  the  axone,  and  are  distributed  to 
other  cells  by  way  of  its  collaterals. 

The  reflex  arc. — A  pair  of  these  complemental  neurones, 
afferent  and  efferent  in  function,  in  contact  by  their  inner 
ends,  and  reaching  outward  the  one  to  a  receptor  and  the 
other  to  a  muscle  or  gland,  constitute  a  simple  reflex  arc. 
This  is  the  unit  of  organization  within  the  nervous  system 
It  is  a  simple  mechanism  for  the  functions  indicated  in  our 
diagram  on  page  436.  It  was  named  a  reflex  arc  because  it 
appeared  to  be  a  pathway  over  which  the  effect  of  a  stim- 
ulus sent  to  a  center  is  reflected  back  in  action  to  view. 
Figure  259a  shows  such  an  arc  for  the  body  of  a  vertebrate. 
The  afferent  cell  body  {u)  lies  in  the  ganglion  on  the  dorsal 
root  of  a  spinal  nerve;  its  dendrites  (not  shown)  are  in  the 
skin ;  its  axone  enters  the  cord .  The  efferent  cell  body  (v)  lies  in 
the  gray  matter  of  the  spinal  cord;  its  dendrites  are  in  contact 
with  termini  of  the  axone  of  the  other  cell,  and  its  axone 
proceeds  outward  through  the  anterior  root  of  a  spinal  nerve 


RESPONSIVE   LIFE  OF  ORGANISMS 


451 


to  end  in  a  muscle.  This  is  a  simple  and  direct  nerve  ])ath, 
sufficing  for  the  reception  of  a  stimulus  and  the  development 
of  an  appropriate  automatic  response. 


^ 1  7r^ 


Fig.  259  Diagram  of  reflex  arcs  in  the  spinal  cord,  a,  a  simple  reflex  arc  shown 
in  half  the  spinal  cord  in  cross  section.  6,  a  direct  connection  of  one  aff'erent 
with  a  number  of  efferent  neurones,  c,  indirect  connection  through  a  neurone 
intercalated  in  the  arc.  u,  afferent,  v,  efferent  fibers,  x,  intercalated  tract  cell 
in  the  cord,      (a,  after  Howell,  b  and  c  after  Kolliker) 

But  there  are  no  nerve  paths  quite  so  simple  and  indepen- 
dent as  indicated  by  this  diagram.  There  are  always  by- 
paths which  a  stimulus  may  take  to  reach  other  efferent  cells 
and  to  produce  multiple  response.  These  bypaths  may  be 
provided  by  various  modes  of  branching  within  the  nerve 
centers;  by  cgllaterals  as  indicated  in  figure  259/^,  or  by 
intercalated  nerve  cells  that  lie  wholly  within  the  nerve 
centers  as  indicated  in  figure  2^gc.  By  reason  of  such  con- 
nections a  stimulus  on  a  single  receptor,  may  according  to 
its  strength,  give  rise  to  impulses  in  many  motor  nerves. 

The  nervous  system  is  a  unit.  No  reflex  arc  exists  by 
itself  alone.  All  the  circuits  of  the  body  are  connected,  in 
the  first  instance  by  collaterals  and  dendrites,  and  in  the 
next,  by  the  arborisations  of  additional  nerve  cells  inter- 
calated within  the  nerve  centers.  Even  in  so  lowly  an 
animal  as  the  earthworm,  in  whose  segments  the  several 
ganglia  appear  to  exercise  a  degree  of  independence  and 


452  GENERAL  BIOLOGY 

autonomy,  there  are  abundant  paths  leading  to  adjoining 
segments,  ultimately  connecting  all  the  segments  together. 
If  one  imagine  the  two  ganglia  shown  in  figure  109  (page 
173)  to  be  packed  (as  in  fact  they  are  packed)  with  cells  of 
the  several  types  that  are  shown  singly  in  that  figure,  he  will 
readily  conceive  how  numerous  are  the  paths  of  possible 
communication  by  contact  between  the  nerve  cells. 

But  the  existence  of  a  bypath  does  not  mean  that  a  nerve 
impulse  must  always  follow  it.  There  are  mam-travelled 
roads,  as  well  as  bypaths  in  the  nervous  system.  A  stimu- 
lus at  any  given  point  has  its  accustomed  path  which  it 
always  follows;  whether  it  shall  overflow  into  its  possible 
bypaths  is  apparently  determined  largely  by  its  intensity. 
A  finger  prick  if  slight  enough  may  merely  cause  the  finger  to 
be  lifted  in  response;  thus  but  a  few  muscles  will  be  called 
into  action.  But  a  more  vigorous  stimulus  at  the  same 
point  may  cause  the  arm  to  be  jerked  back,  involving  the 
action  of  many  muscles:  and  a  deep  puncture  at  the  same 
point  may  initiate  nervous  impulses  vigorous  enough  to  over- 
flow into  most  of  the  motor  circuits  of  the  body,  calling  the 
whole  muscular  system  into  action.  This  also  may  be 
likened  by  analogy  to  the  distribution  of  stimulating  news 
by  telegraph.  A  slight  accident  excites  but  a  little  local 
interest  among  the  few  people  who  are  most  directly  involv- 
ed, but  a  war  scare  may  set  the  wires  going  in  every  impor- 
tant telegraph  office  in  the  country.  There  is  a  mechanism 
at  hand  for  communicating  with  all  the  motor  circuits  in 
the  organism ;  but  only  so  much  of  it  is  used  as  is  warranted 
by  the  nature  of  the  stimulus. 

Doubtless  these  paths  of  nervous  communication  have 
had  a  gradual  evolution,  and  have  been  formed  to  meet  the 
needs  of  the  organism  during  its  long  past  history.  For 
they  lead  in  the  direction  of  harmonious  and  well 
co-ordinated  action.     All  the  muscles  that  may  be  called 


RESPOXSIVE  LIFE   OF  ORGAXISMS  453 

into  action  by  a  single  stimulus,  work  together  concordantly 
to  produce  results  that  are  in  general  beneficial.  Differen- 
tiation of  parts  and  the  development  of  a  mechanism  for 
intercommunication  between  the  parts  would  be  of  nu  use 
without  coordination.  Coordination  is  illustrated  by  any 
act  that  is  neatly  performed;  all  the  muscles  pull  at  the 
right  tension,  at  the  right  time  and  in  the  right  order. 
Want  of  coordination  appears  when  the  nervous  system 
"goes  to  pieces,"  as  in  convulsions;  or,  when  some  unusual 
stimulus  is  applied;  something  of  it  is  seen  even  as  a  result 
of  tickling,  which  may  produce  useless  and  unregulated 
movements. 

Control  circuits. — Coordination  in  the  nervous  system 
tends  to  centralization.  So  long  as  the  ganglia  are  of  equal 
potency  the  effect  produced  in  one  by  a  stimulus  at  one 
point  of  the  body  may  be  opposed  by  the  effect  produced  by 
another  stimulus  at  a  distant  point.  A  homely  but  familiar 
experience  shows  how  stimuli  may  interfere  with  each  other. 
If  a  stimulus  in  our  nose  (which  may  be  accompanied  by  a 
tickling  sensation)  be  impelling  us  to  sneeze,  we  may  start  a 
countervailing  stimulus  by  vigorous  pressure  upon  the  upper 
lip,  and  thus  we  may  keep  from  sneezing.  Stimuli  are  not 
of  equal  importance,  nor  is  their  importance  always  propor- 
tioned to  their  intensity.  A  vibratory  stimulus  of  very 
slight  intensity  coming  in  the  form  of  light  to  the  eye  may 
reveal  the  near  approach  of  a  powerful  enemy.  It  is  im- 
portant that  the  animal  heed  this  stimulus  and  make  its 
escape,  even  though  appealed  toby  the  presence  of  food  or  of 
other  congenial  circumstances.  It  must  run  now;  it  may 
eat  again.  In  other  words,  it  is  often  important  that  all  the 
activities  of  an  animal  be  concentrated  on  accomplishing  a 
single  purpose — be  it  escape  or  defense;  it  is  a  matter  of  life 
or  death.  Hence  some  part  of  the  nervous  system  must 
dominate  the  other  parts  to  the  extent  of  determining  what 


454 


GENERAL  BIOLOGY 


stimuli  shall  be  heeded,  and  toward  what  ends  all  the  activi- 
ties of  the  body  shall  be  directed.  If  there  can  be  a  head- 
quarters to  which  all  stimuli  of  this  nature  shall  be  referred, 
and  from  which  the  dominating  impulses  shall  go  out  to  the 
muscles,  the  resulting  action  may  be  more  efficient. 

The  mechanism  for  such  control  appears  to  have  been 
found  in  the  derived  circuits  within  the  nerve  centers.  We 
have  already  noted  that  besides  the  nerve  cells  composing 
the  reflex  arcs,  there  are  other  cells  within  the  centers,  that 
are  situated  as  intermediaries  between  the  primary  circuits. 
These  have  developed  secondary  circuits  of  their  own;  and 
we  have  also  noted  that  these  are  the  media  of  distribution 
of  stimuli  in  case  of  multiple  responses.  A  single  reflex  arc 
is  sensitive  to  but  one  kind  of  stimulus  and  tends  of  itself 
alone  ahvays  to  give  but  one  kind  of  response;  but  these 
secondary  circuits  are  so  situated  that  they  have  to  respond 
to  varied  stimuli  coming  from  every  quarter — sometimes 
augmenting  each  other,  sometimes  interfering  with  each 
other.  We  may  not  be  able  to  say  how  they  control  action, 
but  we  may  well  believe  that  their  intermediary  position  is 
advantageous  in  determining  what  shall  be  the  totality  of 
the  organic  response. 

Among  these  secondary  circuits  are  innumerable  lines  of 
possible  communication  (through  points  of  mutual  contact), 
and  action  is  determined  by  the  paths  the  stimuli  take.  If 
the  stimuli  follow  paths  that  lead  to  useful  and  beneficial 
action  the  animal  may  live  to  have  the  like  occur  again  and 
again,  until  a  main-travelled  road  for  such  stimuli  is  estab- 
lished, and  the  action  becomes  habitual.  If  on  the  other 
hand,  the  stimulus  should  follow  unprofitable  paths,  leading 
up  to  the  wrong  action,  it  might,  if  the  mistake  were  serious, 
lead  to  death  (if,  for  example,  a  skunk  seeing  an  approach- 
ing train,  should  fail  to  get  off  the  track) .  Thus  the  struc- 
ture of  these  secondary  circuits  is  such  as  to  furnish  a  means 


RESPONSIVE   LIFE  OF  ORGANISMS 


455 


of  controlling  and  coordinating  responses  that  may  be  quite 
as  automatic  as  the  action  of  the  reflex  arcs  themselves. 
When  varying  or  conflicting  stimuli  come  in,  which  shall 
have  the  right  of  way  is  determined  by  the  availability  of  the 
paths  these  secondary  circuits  furnish. 

Cephalization. — It  has  come  about  in  the  development  of 
all  the  higher  animals  that  the  most  specialized  of  the  sense 
organs  have  been  located  at  the  front  end  of  the  body;  and 
doubtless,  this  fact  has  determined  the  location  of  the  con- 
trol center.  The  end  of  an  animal  that  goes  ahead  first 
comes  into  contact  with  the  new  features  of  environment. 
Here  then  should  be  located  the  organs  that  are  the  best 
agencies  of  discovery;  here,  the  organs  that  are  responsive 
to  stimuli  coming  from  a  distance;  the  eye,  the  ear,  the  nose 
and  the  antennae  of  the  arthropods.  Such  organs  as  these 
can  give  knowledge  of  the  presence  of  an  enemy  before  their 
possessor  has  fallen  into  its  grasp;  they  can  locate  food  or 
shelter  or  kindred,  that  might  be  passed  by  blindly.  It  is 
most  natural,  therefore,  that  the  part  of  the  central  nervous 
system  with  which  these  "distance  receptors"  are  most 
directly  connected  should  gradually  assume  the  regulative 
function. 

The  brain  is  primarily  an  aggregate  of  neurones.  These 
consist  of  the  same  parts  as  the  other  neurones — cell  bodies, 
dendrites  at  the  receiving  end,  and  axones  at  the  other  end 
— and  they  are  combined  together  in  circuits,  and  connected 
more  or  less  directly  with  all  the  other  circuits  of  the  body. 
They  have  been  from  the  beginning  most  directly  connected 
with  the  organs  of  special  sense  in  the  head;  hence  they  are 
well  used  to  receiving  important  stimuli  from  these  organs 
of  outlook,  and  of  discharging  impulses  to  every  part  of  the 
nervous  system.  Certain  of  these  stimuli  have  always  been 
of  paramount  importance  to  the  organism  and  well  worn 
paths  have  been  established  for  them.     So,  actions  that  are 


456  GENERAL  BIOLOGY 

needful,  are  readily  brought  about.  The  nerve  impulses 
that  will  bring  them  to  pass  find  established  channels 
through  the  well  integrated  mass  of  neurones  comprising  the 
nervous  system,  and  they  run  through  these  channels, 
obliterating  the  effects  of  other  unimportant  stimuli. 
Thus,  we  have  a  mechanism  which  furnishes  the  conditions 
for  a  great  variety  of  responses,  and  that  may  be  organized 
by  experience   for  the  ready   performance  of   specific  acts. 

Such  a  nervous  equipment  suffices  for  the  carrying  out  of 
reactions  that  are  determined  by  sense  perception  automati- 
cally, the  right  of  way  being  given  to  the  kind  of  stimuli 
that  in  the  past  development  of  the  system  have  determined 
its  paths.  The  paths  are  redeveloped  in  successive  genera- 
tions. The  mechanism  is  perfected  with  the  survival  of  the 
fittest,  at  least,  with  the  elimination  of  the  unfit,  or  ill  ad- 
justed. Such  a  mechanism  gives  reactions  that  are,  there- 
fore, wonderfully  adapted  to  the  particular  set  of  circum- 
stances under  which  they  have  been  developed;  but  they 
are  inexorably  fixed  in  the  structure  of  the  nervous  system. 

Such  reactions  characterize  the  habits  of  most  of  the  lower 
animals.  The  moth  that  flies  to  a  candle  flame  is  stimulated 
irresistibly  by  the  light.  Its  ancestors  for  ages  have  flown 
to  white  objects  (flowers)  at  night.  In  a  proper  environ- 
ment there  is  nothing  better  for  a  moth  to  do  than  this. 
Thus,  it  gets  its  living.  But  candles  being  introduced  into 
its  environment,  it  flies  to  a  candle,  not  being  able  to  distin- 
guish between  candle  light  and  the  light  reflected  from  a 
flower,  or,  at  least  not  being  able  to  respond  differently,  or 
even  to  withhold  response.  Hence,  although  it  may  be 
merely  singed  with  the  first  c^'^tact,  it  repeats  the  act  so 
long  as  it  is  able  to  respond  to  the  light  stimulus.  Thus  it 
goes  down  before  a  peril,  new  to  its  racial  experience,  and 
not  provided  for  in  its  nervous  organization.  If  candle 
lights  were  to  become  universal,  its  race  would  be  doomed  to 


RESPONSIVE  LIFE  OF  ORGANISMS  457 

extinction,  unless,  perchance,  some  line  of  descent  should 
break  away  from  traditional  habits,  by  developing  some  new 
paths  of  action. 

Brain  action  is  not  necessarily  a  whit  less  automatic  than 
the  action  of  a  reflex  arc.  The  moth  has  a  brain,  but  it  does 
not  learn  in  this  instance  by  experience.  If  past  experience 
is  reproduced  at  all  in  memory,  the  impulses  arising  from  it 
are  powerless  to  check  those  that  arise  from  the  next  percep- 
tion of  light.  Control  here  is  based  on  racial — not  at  all  on 
individual — experience. 

A  mechanism  for  adaptation  in  the  individual. — The 
growth  of  the  control  centers  in  the  nervous  system  has  ever 
meant  a  multiplication  of  new  channels  of  intercom- 
munication between  the  added  neurones  in  them.  It  has 
meant  the  development  of  accessory  circuits  not  directly 
responsible  for  the  ordinary  activities  of  the  body.  It  has 
meant  more  and  ever  more  by-paths,  which  peripheral 
stimuli  might  or  might  not  traverse. 

The  primary  function  of  reflex  response  not  being  required 
of  these  accessory  circuits,  they  have  taken  on  new  functions 
of  their  own,  and  have  assumed  new  powers  of  control. 
Especially  in  the  cerebral  hemispheres  of  the  vertebrate 
brain,  where  they  reach  their  best  development,  they  have 
come  to  preside  over  most  of  the  activities  of  the  body. 

The  neurones  of  the  body  are  by  no  means  to  be  con- 
sidered merely  as  mechanical  agents  of  intercommunication; 
they  are  all  living  cells,  having  their  own  metabolism,  con- 
suming food  and  developing  energy,  which  may  manifest 
itself  in  more  than  one  way.  They  act  upon  each  other  as 
upon  the  other  tissues  of  the  body,  in  and  of  themselves, 
whether  stimulated  from  without  or  not;  and  it  is  natural, 
therefore,  that  the  masses  of  neurones  that  make  up  the  con- 
trol centers  should  manifest  themselves  in  new  ways. 
Their  dendrites  are  combined  in  innumerable  paths,  and 


458  GENERAL  BIOLOGY 

although  not  reached  directly  by  a  single  external  stimulus, 
they  are  so  connected  with  the  peripheral  circuits  of  the 
body  as  to  be  within  the  reach  of  all ;  and  they  may  be  in- 
fluenced by  all.  Just  how  the  circuits  of  the  upper  brain 
are  influenced,  we  may  not  say,  but  apparently  the  results 
of  these  influences  are  more  lasting  here  than  in  other  parts 
of  the  nervous  system.  The  effect  of  a  given  stimulus  is  no 
longer  an  unvarying  impulse  and  action.  In  the  labyrinth 
of  brain  paths  the  stimulus  sets  off  the  whole  chain  of  im- 
pulses that  have  followed  upon  it  in  the  past  and  the 
pleasurable  or  painful  results  of  past  experience  are 
recalled  in  memory  along  with  the  stimulus;  if  pleasurable, 
the  natural  impulses  that  go  with  the  stimulus  may  be 
allowed  to  go  on  to  fulfillment;  if  painful,  the  neurones  of 
the  new  center  possess  the  power  to  direct  action  into  new 
channels. 

A  child  on  seeing  for  the  first  time  a  pretty  bee  upon  the 
window  pane  is  impelled  to  catch  it  and  examine  it  with  his 
hands.  If  allowed  to  do  so,  he  learns  something  about  bees, 
by  the  most  fundamental  of  educational  methods — by  ex- 
perience. The  impulse  to  touch  the  bee  and  the  painful 
impressions  that  imimediately  follow  become  so  intimately 
associated  in  the  accessory  circuits  of  his  brain  that  the  next 
time  he  sees  a  bee  (or  it  may  be,  even  a  fly),  on  the  window 
pane  the  sight  of  it  immediately  sets  off,  along  with  the  im- 
pulse to  touch  it,  other  countervailing  impulses  arising 
out  of  the  memory  of  the  former  experience.  Thus  the 
new  control  center  steps  in  and  prevents  the  expected 
action  by  initiating  new  ones. 

Perhaps  we  may  be  permitted  to  compare  this  new  con- 
trol center  to  the  referee  at  a  game.  He  is  not  necessary  to 
the  progress  of  regular  play,  but  he  may  with  advantage 
step  in  and  control  the  action  in  case  of  conflict,  or  of  the 
appearance  of  unsolved  difficulties. 


RESPONSIVE  LIFE  OF  ORGANISMS 


459 


The  development  of  the  cerebrum  as  an  organ  of  memory 
is  the  last  and  greatest  step  in  the  development  of  the  sen- 
sory mechanism  in  vertebrates.  It  makes  education  possi- 
ble. Modes  of  action  may  be  altered  in  the  lifetime  of  the 
individual,  and  new  modes  of  action  may  be  tried  and  if 
found  well  approved  by  results,  may,  by  repetition,  be 
made  habitual.  And  it  should  be  clearly  apprehended  that 
the  new  control  center  does  not  replace  the  old.  The  in- 
dividual has  his  lower  reflex  apparatus  and  correlation  cen- 
ters in  charge  of  the  ordinary  operations  of  his  body  that  are 
necessary  to  keep  life  going,  and,  superadded  thereto,  he  has 
the  new  part  by  means  of  which  he  may  continually  be  im- 
proving his  adaptation  to  environment. 

These  then  are  the  steps  we  have  tried  to  trace  in  the  per- 
fecting of  the  nervous  system  as  a  seat  of  the  sentient  life : 

i)  The  differentiation  among  the  cells  of  the  primitive 
metazoan  of  a)  receptors  (sense  organs) ;  b)  contracting  cells 
(muscles),  and  c)  communicating  cells  (nerves)  connecting 
the  other  two  sorts. 

2)  The  withdrawal  of  the  nerve  cells  from  the  surface  of 
the  body  to  protected  situations  in  the  interior,  and  their 
association  together  to  form  ganglia. 

3)  The  differentiation  of  neurones,  bearing  axones  and 
dendrites,  and  the  development  of  polarity  in  them. 

4)  The  differentiation  of  neurones  into  two  complemen- 
tal  sorts,  and  the  association  of  these  in  pairs,  forming  reflex 
arcs,  each  pair  joining  sense  organ  to  muscle  or  gland. 

5)  The  development  of  intercalary  cells  in  the  nerve 
centers,  serving  by  their  own  intercommunicating  processes 
to  bind  together  the  reflex  circuits  of  the  body. 

6)  The  development  of  specialized  sense  organs,  in  con- 
nection with  some  of  the  ganglia  at  the  front  end  of  the 
body. 


46o  GENERAL  BIOLOGY 

7)  The  development  of  coordination  centers  (groups  of 
integrated  accessory  circuits)  among  the  added  neurones  of 
the  principal  centers. 

8)  The  development  of  control  centers  in  connection 
with  ganglia  at  the  front  end  of  the  body,  establishing  a 
brain. 

9)  The  development  of  the  upper  brain  as  the  chief  con- 
trol center  of  vertebrates. 

Relations  hetiveen  parts  and  functions  in  the  nervous  system 

of  vertebrates. 

We  have  already  given  very  brief  consideration  to 
the  parts  in  the  nervous  system  of  the  salamander,  (general 
structure,  pages  188-192;  development,  pages  195- 
201).  Essentially  the  same  features  of  both  structure  and 
development  characterize  all  the  higher  vertebrates.  The 
same  parts  are  present  and  in  the  same  relations,  and  they 
come  into  existence  by  the  same  developmental  processes. 
The  relatively  greater  development  of  the  higher  centers  of 
the  brain  has  also  been  suggested  (see  figure  128  on  page 
201).  Figure  260  shows  roughly  the  location  of  the  princi- 
pal parts  of  the  nervous  system  in  the  human  body.  Brain 
and  spinal  cord  occupy  the  dorsal  axis,  and  cranial  and 
spinal  nerves  connect  these  m_ultiple  centers  with  every  part 
of  the  surface  of  the  body.  The  sympathetic  ganglia  and 
nerves  of  the  organs  of  the  coelom  are  not  shown. 

As  in  the  salamander  so  in  other  vertebrates  each 
spinal  nerve  has  two  roots.  The  ganglion-bearing  posterior 
root  is  a  bundle  of  afferent  or  sensory  fibers  that  bring  in 
the  effects  of  stimuli  from  the  surface  of  the  body,  and 
the  anterior  root  is  a  bundle  of  efferent  (mostly  motor 
fibers,)  that  carry  impulses  to  muscle  or  gland  (or,  through 
the  ventral  commissures,  to  the  ganglia  of  the  sympa- 
thetic system).     The  bodies  of  the  afferent  neurones,  as  we 


RESPONSIVE  LIFE   OF  ORGANISMS 


461 


have    seen,    compose     the     dorsal      root     ganglion.     The 
bodies  of  the  efferent  neurones  lie  in  the  gray  matter  of 

the  central  part  of  the  cord,  where 
they  are  associated  with  other 
intercalary  nerve  cells.  The 
afferent  fibers  pass  through  the 
white  part  of  the  cord  up-ward 
toward  the  brain  by  several 
routes.  But  the  white  matter  is 
composed  mainly  in  oursehes 
of  fibers  of  intermediary  neu- 
rones, or  of  efferent  fibers  de- 
scending from  the  brain.     These 


fibers    are     arranged     in 


great 


tracts  or  "cokimns,"  which  are 
the  main  lines  of  communica- 
tion between  the  brain  and  out- 
lying ganglia.  Even  the  main 
fiber  tracts  are  too  numerous  for 
us  to  attempt  to  give  an  account 
of  them  here. 

Lying  in  the  pathway  of  some 
of  these  bundles  in  the  base   of 
the  brain  are  some  very  impor- 
tant   masses   of   cells,    that   are 
^      ^^^     T,,  ^        r  centers  of  control  over  the  most 

tiG.   260.     The    nervous    system  of 

man.    (After  Ranke)  vitally    important   proccsscs    of 

the  body.  In  the  midst  of  the  medulla,  for  example,  lie 
the  centers  for  the  control  of  heart  beat  and  respira- 
tion. But  the  greater  part  of  the  cells  of  the  brain  occupy 
the  outer  layer  of  gray  matter  of  the  cerebellum  and  cerebral 
hemispheres.  The  cerebellum  is  connected  in  an  important 
way  with  the  control  and  coordination  of  the  involuntary 
movements  of  the  body,  and  the  cerebrum,  or  upper  brain, 


462 


GEXERAL  BIOLOGY 


is  the  chief  control  center  of  the  voluntary  activities  of   the 
body,  and  the  organ  of  the  mind. 

The  outer  cellular  layer  of  the  hemisphere  is  known  as  the 
cortex.  The  chief  divisions  of  its  topography  as  marked  out 
by  the  convolutions  of  its  surface  are  called  lobes,  some  of 
which  are  named  in  figure  261.     The  distribution  of  the 


Fig.  261.  Diagram  of  the  chief  tracts  of  projection  fibers  of  the  brain.  Roman 
numerals  designate  cranial  nerve  roots  (as  in  fig.  262)  Capital  letters 
designate  fiber  tracts,  as  mentioned  in  text,  p,  pons   (Fiom  Howell,  after  Starr). 

fibers  from  the  cells  that  compose  the  cortex  is  enormously 
complicated,  and  is  not  fully  known,  but  some  of  the  major 
feature^  of  that  distribution  are  indicated  in  the  figure. 
This  shows  some  of  the  main  lines  of  communication  between 
the  principal  centers  within  the  nervous  system.  There  are 
three  principal  sorts  of  fibres  passing  out  from  the  cells  of 
the    cortex    of    the    hemispheres,     i)   commissural    fibers 


RESPONSIVE    LIFE    OF   ORGANISMS 


463 


which  extend  across  from  one  side  to  the  other  joining  Hke 
parts  of  the  two  halves  of  the  brain;  2)  association  fibers, 
which  wholly  within  the  hemispheres  and,  extending 
between  lobes,  connect  one  part  of  a  hemisphere  with 
another  part;  and  3)  projection  libers,  which  connect  the 
cortex  of  the  hemispheres  with  underlying  parts  of  the  brain 
and  with  the  cord.  Only  the  main  tracts  of  projection 
fibers  are  indicated  in  the  diagram.  Some  of  these  fibers 
will  be  seen  to  extend  directly  down  the  cord  (as  the  fibers 
of  the  motor  tract  B,  through  which  the  movements  of  the 
body  are  controlled  at  will),  some  end  in  the  medulla 
(tract  C),  others  in  the  mid-brain  (tract  D),  others  in  the 
pons  (tract  A),  etc.  The  diagram  also  shows  the  three 
main  tracts  that  go  out  from  the  cerebellum,  to  the  mid- 
brain (tract  F),  to  the  pons  (tract  G),  and  into  the  cord 
(tract  H). 

We  have  seen  in  the  salamander  that  the  principal  "dis- 
tance receptors",  eyes  and  ears 
and  olfactories,  are  connected 
directly  with  the  brain.  Figure 
262  shows  the  nerves  of  these 
organs,  and  also  the  other  cranial 
nerves  as  they  occur  in  our- 
selves. 

The  structure  of  the  cortex  of 
the  hemispheres  is  of  very  great 
interest  to  us  because  this  is  the 
highest  control-center  of  the 
body.  An  intelligent  animal 
with  its  cerebral  cortex  removed 
becomes  a  mere  automaton, 
without  volition  or  spontaneity 
7    of  action.     The  nutritive  process 

motor     nerve     of     the     face.      8.  j^g^y  ^o  on  I  COnSCioUSUCSS  is  lost. 

auditory     nerve.      9,     the    glosso-  '■'■'■"■J    S 

pharyngeal   nerve.      10.  the  vagus  YlVe  laVCrS   of   CClls   are   rCCOg- 

nerve.     s,  spmal  nerves.  -^  " 


Fig.  262.  Diagram  of  the  relations 
of  brain  and  cranial  nerves  in 
man.  AI,  medulla,  C,  cerebellum, 
cer,  cerebral  hemisphere.  1 , 
olfactory  nerve.  2,  optic  nerve. 
3  4,  and  6  oculo-motor  nerves^ 
5   sensory   nerve    of    the    face, 


464 


GENERAL  BIOLOGY 


nized  in  the  cortex,  differing  considerably  in  form  and  in 
mode  of  branching  of  their  cell  processes,  as  well  as  in  posi- 
tion, and  all  of  them,  extremely  complicated.  A  single 
cell  from  one  of  the  middle  layers  of  the  human  cortex  is 


Fk;.   263.     A  single  cell  from  the    cerebellar  cortex  of  the  human    brain,     x,  its 
dendrites,     y,  the  cell  body,     z,  the  axone  or  nerve  fiber.     (From  Stohr) 

shown  in  figure  263.  The  most  remarkable  feature  of  it  is 
the  extraordinary  richness  of  the  branching  of  the  dendrites. 
These  are  interlaced  and  come  into  contact  with  the  termini 
of  the  processes  of  other  cells  that  lie  in  other  parts  of  the 
hemispheres,  and  in  other  centers  of  the  brain  and  cord.  In 
the  entire  cortex  there  are  said  to  be  millions  of  such  cells. 
If  here,  as  elsewhere  in  the  nervous  system,  nerve  cell 
processes  are  channels  for  intercommunication — channels 


RESPONSIVE  LIFE  OF  ORGANISMS  465 

for  the  conveyance  of  impulses — how  manifold  are  the  ways 
these  cells  may  react  upon  each  other.  How  inconceivably 
numerous  are  the  by-paths  of  the  brain .  The  mere  mechani- 
cal complexity  of  our  thinking  apparatus  is  beyond  the  com- 
pass of  our  thought. 

Despite  the  differences  in  the  mental  powers  of  verte- 
brates, the  anatomical  differences  of  the  cortex  are  not  very 
great.  Structurally  the  cortex  of  a  rodent  is  very  like  that 
of  a  man.  The  increase  in  number  of  cells  is  not  proportion- 
ate to  the  increase  in  size  in  the  brains  of  the  higher  mam- 
mals; the  increase  appears  to  be  due  rather  to  the  more 
extensive  development  of  cell  processes  and  of  intercellular 
substance,  the  cell  bodies  in  the  cortex  of  the  brains  of  the 
higher  mammals  being  thus  spaced  farther  apart.  The 
mechanism  is  therefore  much  more  alike  than  we  should 
expect,  judging  by  the  great  differences  in  mental  capacity. 
The  analogy  has  been  aptly  drawn,  that  the  structural 
difference  between  a  watch  that  will  not  keep  good  time,  and 
a  perfect  time  piece  may  be  very  slight  indeed. 

Such  is  the  arrangement  of  neurones,  that  every  part  of 
the  cortex  may  receive  impressions  from  other  parts  of  the 
nervous  system  and  every  part  may  give  rise  to  outgoing 
impulses.  In  other  words,  every  point  is  a  center  of  an 
arc,  with  incoming  and  outgoing  paths.  The  brain  is, 
therefore,  essentially  an  integration  of  neurones,  combined 
in  afferent  and  efferent  intercommunication  arcs. 

There  are  no  very  striking  differences  in  structure  in 
different  parts  of  the  cortex,  and  this  in  spite  of  the  fact 
that  the  functional  differences  are  more  or  less  distinctly 
localized.  But  our  knowledge  of  these  "centers"  in  the 
cortex  is  very  imperfect.  Results  have  been  most  readily 
arrived  at  in  the  case  of  the  motor  functions,  because  a 
stimulus  applied  to  a  given  part  of  the  cortex  may  pro- 
duce a  visible  response  in  muscular  movement.     By  this 


466 


GENERAL  BIOLOGY 


means  (as  well  as  by  the  opposite  one  of  observing  the 
paralysis   produced   by    local    injuries)     the    great    motor 

area  that  traverses  both 
hemispheres  (m,  of  fig. 
264),  has  been  carefully 
explored.  The  definite- 
ness  of  the  responses  to 
stimulation  upon  these 
centers  has  been  aptly 
compared  to  that  of  the 
tones  of  a  piano  that 
result  when  certain  keys 
are  struck.  If,  however, 
the  motor  center  for  the 
leg  or  arm  be  stimulated 

Fig.  264.      Diagram  of  localization  of  functions  •  ■hAmicnVif^rf^     fVif^ 

in  the  cerebrum.  M,  medulla.  C,  cerebel-  l^J-  OUC  ncmiSpncrC  Xne 
lum.  ni,  the  great  motor  area  of  the  hemis-  l.-^^-U  ^f  fViP"  n+ViA-r  cir^p.  r,i 
phere  with  a  few  of  the  control  centers  ilHlD  OI  tnC  Otncr  SIQC  OI 
approximately  indicated:  «,  center  for  xi,^  "horlAT-  -ixnil  -moArA-  for 
movements  of  the  leg;  0.  for  arm;  p,  for  face;  ^^^  DOQy  WUi  mOVC ,  lOr 
q,  for  head;  r,  for  organs  of  speech;  t.  center  ^1^  mn-l-or  fiViArc  nf  f  Vi^ 
for  hearing  ("brain  deafness"  may  result  ^'^^  mOIOr  HDCrS  01  XnC 
from  its  injury) ;«,  for  sight ;  t;,  for  smell.         ^^^^^    ^^^^^     g     q£    flgUVe 

261,  (the  "crossed  pyramidal"  tract)  in  the  medulla,  cross 
over  to  the  opposite  side  of  the  body  from  the  one  in  which 
they  originate.  For  this  reason,  also,  great  injury  to  one 
hemisphere  produces  paralysis  of  the  opposite  side  of  the 
body.  Conversely,  the  seat  of  injury,  hemorrhage,  etc., 
within  the  brain  may  often  be  located  by  observing  what 
portions  of  the  periphery  of  the  body  are  paralyzed  or  ab- 
normal in  their  action. 

Study   60.     Demonstration  of  the  functions  of  some  of  the 
principal  parts  of  the  nervous  system  in  the  frog. 

Materials  needed:  Living  frogs,  some  of  them  prepared 
for  this  study  several  hours  in  advance  of  need  (in  order  to 
allow  time  for  recovery  from  the  shock  of  the  operations)  as 


RESPONSIVE  LIFE  OF  ORGANISMS  467 

follows:  some,  with  the  cerebral  hemispheres  carefully 
removed  (other  parts  of  the  nervous  system  being  left  un- 
injured) ;  others,  with  the  cerebellum  also  removed;  others, 
with  the  spinal  cord  severed  at  its  junction  with  the 
medulla,  the  purely  reflex  apparatus  thus  being  isolated. 
Specimens  will  require  to  be  properly  handled  and  cared  for 
until  used.  The  specimens  may  be  used  by  different  stu- 
dents in  succession,  or  if  preferred,  the  demonstration  may 
be  made  by  the  instructor. 

While  the  preceding  account  of  the  nervous  system  has 
followed  logically  the  building  up  of  it,  these  experiments 
will  of  necessity  follow  the  reverse  order.  The  student 
should  first  of  all  be  familiar  with  the  living  normal  frog,  so 
as  to  be  able  to  judge  of  changes  produced  in  its  actions  by 
the  loss  of  brain  parts. 

1.  Observe  a  frog  that  has  lost  its  hemispheres  only, 
noting  especially  its  want  of  volitional  activity.  Test  its 
power  for  correlated  movement  by  throwing  it  into  water 
and  making  it  swim;  by  tilting  the  support  on  which  it 
sits,  making  it  balance  itself;  by  making  it  jump.  Try  to 
determine  experimentally  whether  it  can  see  and  hear. 
See  what  it  will  do  with  a  bit  of  suitable  food  (such  as  a  fly) 
placed  in  its  mouth. 

2.  Try  the  same  experiments  with  a  frog  that  has  lost 
also  its  cerebellum,  noting  especially  the  effect  of  this  loss 
upon  the  coordination  of  its  movements. 

3.  Observe  how  the  severance  of  the  brain  from  the  cord 
has  affected  the  tone  of  the  body  as  a  whole.  Hang  a 
brainless  frog  up  by  its  head  for  convenience  in  manipula- 
tion and  test  its  body  at  various  points  for  reflex  responses 
to  stimulation  of  the  skin.  A  small  brush  dipped  in  dilute 
acid  may  be  used  to  touch  the  skin,  and  the  acid  may  be 
immediately  removed  with  a  wet  sponge. 


468  GENERAL  BIOLOGY 

A  correlation  mechanism  within  the  nerve  centers  that 
remain  may  be  demonstrated  as  follows:  stimulate  one 
side  of  the  frog  in  the  flank  with  the  acid,  and  see  the  foot  of 
the  same  side  lifted  and  rubbed  against  the  spot  as  if  to  wipe 
it  off.  Then  stimulate  the  flank  again  in  like  manner,  but 
hold  the  foot  of  that  side  by  the  toes  to  keep  it  from  repeat- 
ing the  act.  After  one  or  more  attempts  to  use  this  foot, 
the  foot  of  the  other  side  will  be  lifted  and  swung  around  to 
the  spot  stimulated. 

With  an  adjustable  induction  coil  and  a  small  battery, 
try  electrical  stimuli  of  gradually  increasing  strength,  to  see 
the  spread  of  the  effect  with  the  increase  in  intensity  of  the 
stimulus.* 

Stimulate  the  cut  end  of  the  cord;  here  are  the  paths 
coming  down  from  the  brain.  Then  destroy  the  cord  by 
thrusting  a  wire  down  the  vertebral  column  and  twisting  it, 
thus  breaking  up  the  reflex  arcs  and  test  again  for  responses. 

Then  expose  the  great  sciatic  nerve  (it  will  appear  as  a 
coarse  white  thread  lying  between  the  muscles  of  the  inner 
side  of  the  thigh,  and  stimulate  it  directly  to  produce  mus- 
cular response.  Then  trace  this  nerve  to  its  forking  at  the 
knee,  and  stimulate  each  of  ito  main  branches  separately  to 
see  the  specifically  different  responses  resulting. 

The  record  of  thiS  st-cidy  will  consist  of  notes  and  diagrams 
illustrating  th^  nature  of  the  experiments  performed,  and 
their  resulXv«. 


*A  little  strychnine  injected  under  the  skin  with  a  hypodermic 
svi'inge  will  greatly  increase  the  sensitiveness  of  the  spinal  cord  tc 
cutaneous  stimulation :  the  response,  however,  soon  ceases  to  be 
orderly  and  purposeful,  and  becomes  convulsive.  On  the  other 
hand  a  few  crystals  of  salt  placed  upon  the  cut  end  of  the  cord 
will  check,  and  after  a  little  time,  inhibit  altogether  the  reflex 
responses:  the  effect  will  however  soon  disappear,  upon  washing 
the  salt  off  with  normal  saline  solution. 


RESPO:^SIVE  LIFE  OF  ORGANISMS  469 

J.     Types  of  sensory  phenomena. 

The  powers  of  animals  find  expression  in  the  responses 
they  make  to  the  external  world  *  The  great  differences 
we  have  seen  in  complexity  of  nervous  organization  are 
more  or  less  closely  accompanied  by  differences  in  mental 
powers,  manifest  in  behavior.  Every  step  in  integration  of 
the  nerve  paths  of  the  body  is  doubtless  accompanied  by 
improvement  in  action.  Without  attempting,  however, 
to  draw  a  close  parallel  between  organization  and  behavior, 
we  will  now  examine  some  types  of  animal  activity,  that  at 
least  show  steps  of  progress. 

Automatic  unvarying  activities.— Two  examples  of  invary- 
ing  response  have  already  been  before  us  for  consideration. 
The  avoiding  reaction  of  the  protozoan  Paramoecium  as  we 
have  seen,  constitutes  almost  the  entire  stock-in-trade  of 
reactions  for  that  animal.  The  distance  of  movement  back- 
ward upon  stimulation  and  the  extent  of  the  swing  to  the 
aboral  side  will  depend  somewhat  on  the  strength  of  the 
stimulus;  but  the  one  sort  of  reaction  follows  upon  almost 
every  sort  of  vigorous  stimulus  that  the  environment  of  the 
animal  normally  offers.  And  with  repetition  of  the  stimu- 
lus, the  reaction  is  repeated  indefinitely,  and  in  essentially 
the  same  manner.  The  reaction  of  the  moth  to  the  candle 
flame  is  essentially  of  the  same  invarying  type,  although  it 
is  performed  by  the  aid  of  a  complicated  nervous  system. 
The  moth,  however,  has  other  less  inflexible  responses  that 
it  makes  to  other  less  dominating  stimuli. 

Responses  automatically  varying. — The  repetition  of  a 
stimulus  usually  brings  about  a  change  in  the  behavior  of  an 
organism,  sometimes  an  augmentation  of  the  reaction, 
sometimes  the  entire  cessation  of  it.  A  stentor,  for  exam- 
ple, if  stimulated  by  mechanical  contact  with  the  cilia  of  its 


*The  essence  of  an  animal  is  in  what  it  docs. — Aristotle. 


470 


GENERAL   BIOLOGY 


peristome,  will,  for  a  time,  merely  withdraw  its  body  by 
direct  contraction.  If  at  each  extension  the  stimulus  be 
repeated,  the  stentor  will  swing  its  body  first  to  one  side 
and  then  to  the  other.  If  this  be  unavailing  and  the  stimu- 
lus be  continued,  the  animal  will  free  itself  from  its  support, 


ARISTOTLE 

(384-322  B.  C.) 

Naturalist  and  Philosopher. 

and  swim  away.  This  method  of  avoidance  is,  however, 
quite  automatic.  If  the  stentor  be  again  stimulated  when 
it  has  attached  itself  in  a  new  place  it  w411  go  again  through 
the  entire  series  of  varying  responses  under  the  same  stimu- 
lation.    It  learns  nothing  by  the  repetition. 


RESPOXSIVE  LIFE   OF  OROAXISMS  471 

On  the  other  hand  a  stentor  wiU  soon  cease  altogether  to 
react  to  hght  touches  rapidly  repeated.  A  hydra  also  will 
react  to  touch  by  contracting  its  body,  and  if  allowed  time 
between  stimulations  for  complete  extension  of  its  length,  it 
will  contract  again  when  touched,  every  time;  but  if  the 
touch  is  repeated  before  a  full  extension  of  the  body,  the 
animal  will  soon  cease  to  notice  it  altogether.  In  such  an 
organism  the  stimuli  must  follow  each  other  in  quick  suc- 
cession if  they  are  to  modify  action.  Certain  spiders 
habitually  drop  from  their  webs  to  the  ground  when  dis- 
turbed. This  is  their  avoidance  reaction,  and  it  doubtless 
carries  them  often  out  of  an  exposed  situation  into  one  of 
less  danger,  and  at  times  enables  them  to  escape  capture  by 
enemies.  A  certain  spider  will  respond,  when  a  large  tun- 
ing fork  is  struck  near  at  hand,  by  dropping  from  its  web. 
But  it  will  cease  to  do  this  (and  to  put  itself  to  the  trouble 
of  climbing  up  again)  after  the  experiment  has  been  repeat- 
ed half  a  dozen  times. 

Moreover,  the  spider  unlike  the  hydra  and  the  stentor  and 
many  others  of  the  lovv^er  animals,  may  after  daily  repetition 
of  this  experience  become  used  to  the  stimulus  of  the  tuning 
fork  and  cease  to  react  to  it  at  all  after  a  considerable  time. 
This  would  seem  to  indicate  growth  in  power  of  discrimina- 
tion between  stimuli;  for  only  an  animal  with  some  such 
power  could  afiord  to  suspend  the  reaction  by  means  of 
which  it  escapes  its  ordinary  enemies. 

Cessation  of  response  to  continued  but  harmless  stimula- 
tion is  a  wide  spread  phenomenon  in  the  reactions  of  animals. 
It  is  too  familiar  for  much  notice  in  ourselves.  We  are  not 
long  conscious  of  contact  with  our  clothing  after  it  is  put  on, 
notwithstanding  that  by  contact  we  get  it  adjusted  properly. 
And  even  admonitions  of  the  worthiest  sort,  too  oft  re- 
peated, we  let  "go  in  at  one  ear  and  out  at  the  other;"  that 
is,  they  go  unheeded.     The  better  the  organization  of  the 


472  GENERAL  BIOLOGY 

psychic  mechanism,   the  more  lasting  appears  to  be  the 
result  of  getting  used  to  a  stimulus. 

Study  6i.  Observations  on  certain  reactions  of  caterpillars. 
Materials  needed:  Living  caterpillars  in  normal  and 
healthy  condition,  and  a  supply  of  their  appropriate  food. 
Silk  worms  (and  mulberry  leaves)  will  do  for  this,  or  almost 
any  of  the  larvae  of  the  larger  butterflies  or  moths.  The 
larvae  of  the  common  milkweed  butterfly  have  been  used 
successfully. 

1.  Study  the  creeping  reactions  of  an  active  caterpillar. 
Observe  first  its  method  of  locomotion.  Then  place  the 
specimen  on  a  reversible  cord  (as,  for  example,  a  bow  cord 
and  note  the  persistence  of  its  almost  unvarying  reaction  to 
the  pull  of  gravity.  It  crawls  upward.  Reverse  the  cord 
betimes,  and  observe  the  result. 

2.  Then  test  the  variability  of  reactions  to  stimuli  such 
as  will  stop  its  crawling;  a  puff  of  breath,  or  a  sharp  rap  on  a 
table  on  which  its  support  is  resting.  Most  caterpillars 
have  a  characteristic  habit  when  stopped  of  turning  the 
head  either  up  or  down.  Determine  by  trial  (using  a  watch 
for  timing)  how  often  it  is  necessary  to  repeat  the  puffs  of 
air  or  the  raps  on  the  table  in  order  that  they  may  fail  to 
elicit  the  reaction. 

3 .  Test  the  time  it  takes  to  inhibit  the  feeding  reaction 
by  substitution  of  unsuitable  food.  Get  a  hungry  cater- 
pillar to  feeding  on  the  margin  of  the  leaf  of  its  proper  food 
stuff,  and  slip  up  beside  the  leaf  a  sheet  of  some  thin  sub- 
stance unsuitable  for  food  (such  as  a  leaf  of  some  other  plant 
which  the  larva  of  itself  will  not  eat,  or  a  sheet  of  paper  or  of 
tinfoil) .  Note  any  evidence  of  dissatisfaction  with  the  sub- 
stitute food.  Then,  allowing  the  caterpillar  to  resume  eat- 
ing the  right  leaf,  determine  by  trial  what  interval  must 
intervene  before  it  will  again  bite  of  the  substitute.     Ob- 


RESPONSIVE  LIFE  OF  ORGANISMS  473 

serve  whether  this  interval  grows  greater  with  repetition. 
Observe  whether  the  number  of  bites  taken  of  the  substitute 
grow  fewer  after  repeated  trials.  If  the  caterpillar  has  a 
memory  for  the  sort  of  experiences  tried,  how  long  can  it 
remember? 

4.  Observe  the  effects  of  bodily  states  on  the  activities 
of  the  caterpillars  by  comparing  their  reactions  when 
hungry  and  when  well  fed;  when  cold  and  when  warm. 

The  record  of  this  study  may  consist  of  an  account  (with 
diagrams)  of  the  experiments  tried,  and  a  brief  statement  of 
the  results. 

Sequences  of  automatic  activities. — We  come  now  to  the 
consideration  of  a  class  of  phenomena  commonly  known  as 
instincts.  These  are  automatic  activities,  amplified  and 
serially  arranged  and  extended  until  they  cover  often  a  large 
part  of  the  life  of  the  individual.  They  are  not  essentially 
different  from  the  simpler  automatic  acts  we  have  just  been 
considering.  A  caterpillar  instinctively  moves  upward  on 
its  food  plant;  but  creeping  is  itself  a  sequence  of  events. 
The  participation  of  many  sets  of  muscles  is  necessary,  and 
these  must  act  successively  and  in  progressive  order.  Each 
movement  is  prepared  for  by  the  one  that  went  before  it. 
The  stimulus  acts  through  the  control  centers.  Not  the 
stimulus,  but  the  state  (position)  of  the  body  determines 
which  foot  shall  first  be  lifted  and  swung  forward. 

Instincts  proper  are  sequences  of  such  actions  the  events 
of  the  series  being  unlike  in  kind  and  unrepeated.  The 
preparation  of  the  caterpillar  for  its  transformations  is  a 
performance  of  this  type.  When  fully  grown  it  ceases  feed- 
ing, crawls  to  a  place  of  security  (usually  away  from  the 
plant  that  has  nourished  it),  spins  a  silken  cocoon  about  its 
body  and  changes  into  a  pupa.  But  before  these  things 
can  occur  it  must  be  full-fed,  it  must  have  a  store  of  material 
for  further  development,  the  rudiments  of  the  adult  organs 


474 


GENERAL  BIOLOGY 


must  have  reached  a  proper  stage  of  development,  and  the 
silk  glands,  now  nearing  the  climax  and  the  end  of  their  use- 
fulness, must  be  charged  with  the  secretion  that  is  to  form 
the  cocoon,  and  a  host  of  other  physical  (somatic)  conditions 
miust  be  fulfilled.  When  fulfilled,  we  may  say,  speaking  in 
figures,  the  ship  of  instinct  is  laden  and  tugging  at  its  cables ; 
its  course  is  laid  out  from  beginning  to  end,  the  points  of 
call,  the  discharges  of  cargo,  the 
bells  that  shall  be  rung  and  the 
whistles  that  shall  blow  are  all 
pre-arranged,  and  only  the 
signal  to  start  is  needed,  to 
initiate  all  the  events  of  the 
voyage.  Nothing  could  more 
plainly  show  the  essentially 
autogenetic  nature  of  respon- 
ses. 

The  bird  builds  her  nest  when 
the  condition  of  body  and  brain 
impels  to  it.  No  stimulus  has 
any  effect  whatever  until  body 
and  brain  are  ready.  Maturity 
must  be  reached,  and  eggs  must 
grow,  and  mating  must  take 
place;  and  when  all  is  ready, 
the  simplest  sort  of  stimulus, 
the  sight  of  suitable  materials 
(straw  or  fiber  or  hair,  not 
conspicuously  different  from  a 
thousand  other  things  the  eye 
might  fall  upon),  serves  to  set 
the  complex  activities  of  nest 

building  going.     The  stimulus  F'J„,;,2-  A  fti^hiy  s^Si"=3 
is  but  the  spark  that  sets  o£E  the     %l,L.''fpLtJ'lTc"BlL^x''"' 


RESPONSIVE  LIFE  OF  ORGANISMS 


475 


powder  in  the  mine.  In  itself  it  may  be  insignificant,  but  in 
its  relations  to  the  organism  it  is  all  important;  for  it  deter- 
mines the  very  conditions  of  existence.  Nest  building  must 
wait  on  the  finding  of  suitable  materials — materials  not 
too  different  from  those  the  sight  of  which  has  elicited  the 
nest  building  responses  in  the  past,  and  all  the  subsequent 
acts  of  rearing  young  wait  on  nest  building.     This  means 

that  the  want  at  any 
point  of  a  stimulus  that 
can  set  off  an  appropri- 
ate action,  blocVs  the 
remaining  acts  of  the 
series  and  leads  to  fail- 
ure. 

The  perfection  of 
instinct  at  its  best  is 
marvellous.  Sequences 
of  acts,  that,  like  nest 
building  and  web  spin- 
ning, are  worthy  to  be 
ranked  as  fine  arts,  are 
performed  perf  e  c  1 1  y 
without  instruction, 
example  or  experience; 
performed,  perhaps  but 
once  in  a  life  time.  The 
method  of  a  caterpillar 
in  spinning  is  as  much 
a  product  of  its  organi- 
zation as  is  the  silk  in 
its  spinning  glands. 
Glands  and  nerve  cells 
Fig.  266.    A  caddisfly    (Haiesus    sp?)   whose  ^rc  aUkc  charged  during 

sitting    posture    suggests  a  half    way    stage  in  rlpA^plnTimrrif  T  Vi  ^ -v 

the  development  of  the  posture  of  Molanna.         ueveiopnicnL.  i  n  e  ) 


476  GENERAL  BIOLOGY 

are  alike  the  end  results  of  a  long  evolution,  with  endless 
adaptations  to  conditions  of  life. 

The  caddisfly  Molanna  (fig.  265)  "sits  close"  on  a  twig, 
its  wings  up-rolled  about  its  lifted  abdomen,  and  all  the 
other  appendages  outspread  against  the  side  of  a  support- 
ing twig  or  trunk.  So  situated  on  jagged  bark  or  amid 
the  stubs  of  a  twig,  it  is  well  nigh  undiscoverable.  The 
flying  Molanna,  settling  instantly  to  this  attitude,  vanishes, 
ghost-like,  from  view.  It  makes  no  superfluous  motions 
to  hold  the  eye;  actions,  attitude  and  color  are  in  protective 
accord.  But  perfected  actions,  like  structures,  have  to  be 
evolved.  Halesus,  (fig.  266)  sits  in  a  position  intermediate 
between  that  of  Molanna  and  the  more  ordinary  rest- 
ing attitude  of  such  insects;  and  its  posture  suggests  pos- 
sible stages  in  the  development  of  Molanna's  perfected 
habit.  An  ingrained  habit  may  persist,  also,  like  a  vestigial 
organ  after  it  has  ceased  to  be  of  any  use.  Perhaps  the 
most  familiar  illustration  of  this  is  the  turning  round  and 
round  of  a  dog  before  it  lies  down.  The  primitive  dog 
presumably  made  its  lair  in  the  grass,  where  this  was  an 
eminently  useful  performance. 

Instincts  illustrate  extreme  specialization  in  the  neural 
mechanism.  It  is  fitted  finely  to  one  set  of  conditions, 
and  is  apt  to  be  found  wanting  when  conditions  are  altered. 
The  moth  that  flies  to  the  candle  flame  has  left  the  beaten 
track  of  its  ancestry,  through  want  of  discrimination  be- 
tween stimuli.  Another  example  is  furnished  by  the  kinglet 
(fig.  267)  which,  being  racially  unacquainted  with  the 
dangerous  hooks  on  the  burdock  (an  imported  weed), 
endeavors  to  get  the  seed-eating  larvae  from  the  heads  for 
food.  Fatal  want  of  discrimination  is  sometimes  displayed 
toward  objects  of  the  normal  environment.  Thus  the  flesh 
fly  is  stimulated  by  the  odor  of  the  carrion  flower  and  lays 
eggs    upon  the    plant,    where  her   young  on  hatching  will 


RESPONSIVE  LIFE  OF  ORGANISMS 


477 


find  no  food.  The  fly  does  not  possess  even  such 
perceptive  faculties  as  would  enable  it  to  distinguish 
between  a  flower  and  a  dead  carcass.  The  fly  knows  neither 
carcass  nor  flower,  but  only  a  certain  kind  of  olfactory 
stimulus  that  may  come   from  either. 


Fig.  267.      A  mistake  of  instinct.      The  kinglet,  seeking  the  larvit  of    the  burdock 
moth  (see  fig.  247  on  page  425)  is  ensnared  by  the  hooks  of  the  burdock  heads. 


Study   62. 


Experiments  on   the  case  building   instincts  of 
caddis-worms. 


Materials  needed:     A  supply  of  living  caddis-worms,  that 
may  be  kept  in  proper  receptacles  at  proper  temperature 


478 


GENERAL  BIOLOGY 


and  in  good  condition  for  at  least  a  week.  Almost  any 
species  that  makes  its  cases  of  pieces  of  wood  (fig.  268),  or 
stones,  with  or  without  ballast-pieces  attached  to  the  side, 
will  do.  For  the  following  experiments,  handle  the  larvae 
gently,  with  care  not  to  do  them  any  physical  injury,  and 
leave  them  in  clean  water  and  comfortable  conditions  while 
waiting  the  results  of  the  experiments.  While  cutting  cases 
the  larvae  may  be  temporarily  removed  from  them,  if  this  be 
deemed  necessary. 

Observe  the  fitness  of  the  cases  for  protection  of  the  body 


Fig.  268.     A'caddis-worm  (Halesus  sp?)  and  the  case  from  which  it  was  removed. 

(Drawings  by  Mrs.  J.  H.  Comstock). 

and  for  escaping  observation  when  in  the  natural  environ- 
ment. Observe  the  ordinary  activities  of  the  caddis-worms; 
the  manner  in  which  they  drag  their  cases  about,  or  retreat 
into  them  when  disturbed.  Drive  a  worm  out  of  its  case 
(by  poking  it  gently  from  the  rear),  and  observe  the  form 
and  structures  of  the  body  and  its  need  of  protection. 

Study  the  case  of  the  species  selected  for  experiment,  its 
materials  and  construction.     Observe  the  cement-substance 


RESPOXSIVE  LIFE  OF  ORGAxXISMS  479 

which  binds  the  other  materials  together;  this  is  the  har- 
dened secretion  from  glands  that  open  through  the  labium 
of  the  larva,  which  exudes  as  a  fluid,  and  hardens  after  con- 
tact with  the  water.  This  secretion  is  all  the  equipment  the 
larva  needs  for  building  or  repairing  its  cases. 

I.     To  test  the  adaptability  of  case  building  to  present 
physical  needs: 

I.)  Cut  a  hole  in  the  side  of  the  case,  exposing  a  vulner- 
able part  of  the  body,  and  see  if  it  will  be  repaired. 

2.)  Slit  a  case  lengthwise,  in  a  narrow  opening  from  end 
to  end  and  leave  it  to  be  repaired. 

3 .)  Cut  a  case  in  two  crosswise,  and  leave  one  part  of  it 
only  on  the  larva  for  repair. 

II.  To  test  the  adaptability  of  case  building  to  con- 
ditions of  environment. 

4) .  Provide  a  background  of  a  different  color  from  the 
natural  one,  (background  may  be  placed  under  the  bottom 
of  a  glass  dish) ,  and  materials  for  case  building  of  suitable 
size  and  of  a  color  to  match  the  background  (strips  and 
bits  of  mica,  glass,  colored  celluloid,  whitewood,  etc.). 
Provide  also  the  materials  ordinarily  used,  but  which  are 
unsuited  to  the  new  background,  being  there  conspicuous 
when  viewed  against  it.  See  what  materials  a  larva,  re- 
moved from  its  case,  uses  for  making  a  new  one. 

5).  Leave  a  larva,  removed  from  its  case,  upon  the  old 
background,  but  provide  it  only  with  case-building  materials 
that  will  be  conspicuous  against  that  background,  and  note 
the   result. 

The  record  of  this  study  will  consist  of  an  illustrated 
account  of  the  experiment,  setting  forth  their  results. 

Learning  by  experience. — Many  of  the  lower  animals  are 
born  educated  almost  to  the  full  extent  of  their  capacity, 
the  possible  lines  of  action  of  their  whole  lives  being  pro- 


48o  GENERAL  BIOLOGY 

vided  for  and  predetermined  in  their  organization.  The 
acts  most  fundamental  to  the  preservation  of  races,  feeding, 
reproduction,  etc.,  are  thus  provided  for  in  the  main  in  all 
animals.  A  kitten  is  instantly  thrown  into  a  paroxysm  of 
defensive  movements  and  attitudes  at  the  first  sight  or  smell 
of  a  dog.  A  chicken  flees  at  the  first  cry  of  a  hawk,  although 
it  may  be  quite  unresponsive  to  the  (to  us  apparently)  simi- 
lar cry  of  a  catbird.  Nature  has  developed  this  nice  dis- 
crimination by  the  elimination  of  the  unresponsive.  Racial 
experience  has  thus  been  incorporated  into  the  organism  in 
such  manner  that  vitally  important  stimuli  dominate  all  the 
activities  of  the  body  and  enable  it  automatically  to  meet 
the  chief  exigencies  of  life.  There  is,  however,  especially  in 
the  higher  animals,  a  field  of  activity  in  which  reactions  are 
less  stereotyped;  more  variable;  and  here  lies  the  oppor- 
tunity for  learning  by  individual  experience.  This  is  so 
large  a  part  of  our  own  life  that  we  have  difficulty  realizing 
how  limited  it  is  in  many  of  the  lower  animals. 

The  sight  of  food  that  is  not  within  reach  may  stimulate  to 
activities  that  are  predetermined  only  for  the  act  of  feeding, 
and  the  processes  of  nutrition ;  not  at  all  for  the  method  of 
getting  at  the  food.  A  horse  confined  in  a  bare  lot,  is 
stimulated  to  a  great  variety  of  activities  by  the  sight  of  the 
green  grass  on  the  other  side  of  the  fence.  He  does  many 
things  that  yield  no  satisfactory  results;  he  pushes,  he 
whinnies,  he  stamps,  he  tugs  at  the  toprail  with  his  teeth,  he 
rears,  etc.  But  by  chance  he  lifts  the  latch  of  the  gate  with 
his  teeth,  and  this  act  is  accompanied  by  pleasurable  results; 
he  sees  the  gate  open.  A^nother  time  he  is  likely  to  concen- 
trate his  efforts  at  the  gate,  and  to  lift  the  latch  sooner,  with 
fev/er  ineffective  efforts.  Every  repetition  of  an  act  makes 
its  subsequent  performance  easier,  especially  when  accom- 
panied by  pleasurable  experiences  accompanying  successful 
performances  of  it.     Soon  he  is  able  to  eliminate  all  the  un- 


RESPONSIVE  LIFE  OF  ORGANISMS  481 

profitable  acts,  and  to  lift  the  latch  at  once;  he  has  learned 
by  trial  and  error. 

So  we  learn  in  infancy  to  walk,  to  talk,  to  play;  and  in 
later  life,  to  acquire  any  wholly  new  accomplishment  with- 
out instruction  or  example. 

Such  learning  is  conditioned  upon  the  possession  of  a 
nervous  mechanism  that  is  capable  of  retaining  the  impres- 
sions accompanying  a  former  act  until  the  stimulus  is 
repeated.  Such  a  mechanism  is,  as  we  have  seen,  the  upper 
brain  in  the  vertebrates.  It  is  an  agency  for  reviving  along- 
side every  important  stimulus  the  impressions  that  have 
accompanied  former  responses  to  the  same  kind  of  stimu- 
lus, action  then  being  determined  in  accordance  with 
whether  these  have  been  pleasurable  or  painful,  whether 
they  have  been  successful  or  unsuccessful  in  attaining  a 
desired  end.  The  details  of  the  process  will  be  made  much 
clearer  by  the  study  of  a  concrete  example. 

Study  6 J.     Learning  by  trial  and  error  in  chicks. 

Materials  needed :  Healthy  young  chickens,  a  week  to  ten 
days  old;  food  and  water  for  the  chickens.  A  labyrinth 
made  on  the  plan  shown  in  figure  269*  (one  for  each  group 
of  eight  or  ten  observers) . 

This  study  consists  in  observations  on  the  details  of  the 
method  of  a  chick  in  learning  the  route  through  the  box 
from  one  end  of  it  to  the  other.  Place  the  chicks  as 
indicated  in  figure  269;  several  of  them  with  plate  of  food 
in  one  end  of  the  box,  and  one  chick  (the  subject  of  the  ex- 
periment) alone  and  without  food  in  the  other  end.  The 
group  will  feed  and  chirp  contentedly,  and  the  other  one, 
moved  by  the  sound  of  their  social  converse  and  by  his 

*This  may  readily  be  constructed  out  of  an  ordinary  wooden 
cracker  box,  by  adding  partial  partitions  to  make  the  passageway, 
I,  2,  3,  4. 


482 


GENERAL  BIOLOGY 


gregarious  instincts,  will  (if  not  too  full-fed)  try  to  get  to  the 
others.  Observe  in  detail  his  methods.  Let  one  person  of 
the  group  of  observers  be  time  keeper,  and  let  the  others 
record  impartially  all  the  efforts  of  the  chick.  These  efforts 
will  follow  each  other,  sometimes  in  such  quick  succession 
that  some  short-hand  method  will  be  required  for  recording 
them.  The  following,  as  inclosed  in  parentheses  after  the 
acts  named,  are  suggested:  walking  about  (w;  repeat  the 
sign  for  each  start  with  change  of  direction) :  calling  to  mates 
or  peeping  (p) :  peering  through  crevices  or  holes  in  the  sides 
of  the  box  (o) :  flying  against  the  sides  of  the  compartment 
( \[ — mark,  or  checkmark  of  any  sort  quickly  made) :  return 
after  entering  the  passage,  from  points  of  record  (1,2  or  3; 


s 

s 

2 

3 

s    ^ 

i)\ 

] 

4 

Fig.  269.  Diagram  of  a  simple  box  labyrinth,  arranged  for  testing  trial  and 
error  in  young  chicks,  s  ss  sss  the  chicks  at  the  start,  one  isolated  from 
the  company.     /,  a  plate  of  food.  /,  2,  j,  4,  points  of  record  in  the  passageway. 

there  will  be  no  return  from  4,  where  the  mates  are  sighted) . 

Mark  the  chicken  that  is  to  be  the  first  subject  of  the 
experiment  in  some  way  (or  note  its  personal  characteristics) 
so  that  the  same  one  may  be  taken  again  for  repetition  of  the 
trial.  Record  all  its  acts  and  the  time  it  takes  to  find  the 
way  to  its  mates.  Return  it  to  the  starting  point  and 
record  again ;  and  repeat  until  it  has  learned  the  passage,  and 
is  able  to  traverse  it  without  much  hesitation  or  delay,  and 


RESPONSIVE  LIFE  OF  ORGAXISMS 


483 


without  any  misdirected  efforts  *  When  learned  thor- 
oughly, make  a  tabular  record  of  the  time  and  efforts 
expended  in  the  process,  by  successive  trials,  as  follows : 


Number 
of 

Spells  of 
peeping 

Walks  with 
change  of 
direction 

Peer'gs 

through 

walls 

Flights 

Returns  from 

Time 

Trial 

I 

2 

3 

ist  trial 

2d  trial 

/ 

Etc 

If  any  considerable  part  of  the  laboratory  period  remains 
after  one  chicken  is  educated  to  the  act,  another  may  be 
tried;  or  the  labyrinth  may  be  altered  or  complicated  and 
the  same  one  re-tried. 

The  record  of  this  study  will  consist  of  a  diagram  of  the 
experiment,  together  with  a  summary  of  the  results  appear- 
ing in  the  table. 

Further  progress. — As  the  chick  has  mastered  one  per- 
formance so  it  may  master  another.  With  repetition  the 
signs  of  effort  disappear  and  those  of  habit  take  their  place. 

It  is  a  long  step  forward  toward  intelligence  when  brain 
circuits  are  able  to  retain  impressions  arising  from  one 
stimulus  long  enough  to  influence  the  action  that  shall  result 
from  the  next  stimulus  of  the  same  kind;  for  then  the 
responses  may  begin  to  take  on  individual  variations.  It  is 
a  still  longer  step  when  the  central  circuits  through  previous 
stimulation  and  mutual  interaction  become  able  to  originate 
like  acts  in  absence  of  the  original  stimuli;  for  here  initiative 
comes  in.     Then,  the  trial  of  a  performance  need  not  wait 


*It  is  best  that  the  chicken  should  be  quite  unmolested  by  the 
observers  during  the  experiment,  but  if  unfortunate  conditions 
should  have  made  it  sluggish  in  action  (so  that  it  incHncs  to  squat 
and  do  nothing),  results  may  still  be  had  by  apj)lying  any  sort 
of  gentle  stimulus  that  does  not  tend  to  urge  it  in  any  particular 
direction,  such  as  dropping  the  end  of  a  cane  against  the  bottom 
of  the  box. 


484 


GENERAL  BIOLOGY 


upon  an  outside  stimulus;  an  autogenetic  one  may  be  sub- 
vStituted.  Practice  may  go  forward.  Experiments  may  be 
tried.  The  individual  may  of  himself  learn  new  modes  of 
action. 


Fig.  270.      The  Orang     (after  Bos). 


RESPONSIVE  LIFE  OF  ORGANISMS  485 

II.     THE  RESPONSIVE  LIFE  OF  THE  HUMAN  SPECIES. 

Man  in  the  organization  of  his  body  is  a  vertebrate  animaL 
So  great  is  his  Hkeness  in  structure  to  other  vertebrates,  we 
should  have  no  trouble  identifying  every  organ  in  his  body 
from  the  study  of  the  organs  of  the  others.  The  functions 
of  the  parts,  too,  are  so  similar  that  our  knowledge  of  human 
physiology  has  largely  been  derived  from  the  study  of  other 
vertebrates — much  of  it  even  from  the  study  of  one  so  dis- 
tantly related  as  the  frog.  But  the  slight  physical  differ- 
ences existing  between  man  and  even  the  highest  mammals 
are  accompanied  by  mental  differences  so  profound  that 
our  account  of  the  responsive  life  of  organisms  would  be 
most  inadequate  without  brief  notice  of  mental  develop- 
ment in  the  human  species. 

I.     The  natural  history  of  man. 

We  have  not  time  to  review  the  physical  history  of  the 
human  body,  its  development  from  an  egg,  its  segmen- 
tation, its  development  of  gill  clefts  and  a  fish-like 
circulation  that  is  subsequently  altered  to  the  mammalian 
type,  its  nurture  through  embryonic  membranes,  its  birth, 
like  that  of  any  other  marnxmal.  These  do  not  need  to  be 
repeated.  And  we  will  not  make  mention  of  his  mammalian 
affinities,  for  these  are  sufficiently  apparent.  We  will  only 
remark  in  passing  that  man's  nearest  zoological  allies  are 
found  among  the  anthropoid  apes.  The  mammalian  order 
Bimana,  (two  handed  animals),  which  a  distinguished 
zoologist  of  a  past  generation  once  erected  as  a  pigeon-hole 
in  which  man  might  be  kept  apart  from  the  higher  apes 
(Quadrumana;  four  handed  animals),  has  long  been  merged 
in  the  great  mammalian  order  Primates,  which  includes, 
besides  man  and  the  apes,  also  the  monkeys  and  the  lemurs. 
The  zoological  differences  between  man  and  the  higher  apes, 
such  as  the  orang,  the  chimpanzee  and  the  gorilla,  are  far 
less  than  the  differences  between  these  and  the  lemurs. 


486 


GENERAL  BIOLOGY 


Distinguishing  human  characters. — The  chief  features  of 
man's  body  that  distinguish  him  from  his  nearest  allies  are 

precisely  those  that  have 
favored  his  great  psychic 
development;  his  erect  at- 
titude, his  hand  and  his 
brain. 

Man  is  the  only  mammal 
that  stands  erect.  His  legs 
are  longer  and  stronger  and 
his  pelvic  bones  are  stouter 
and  better  consolidated  to- 
gether for  bearing  the  entire 
weight  of  the  body.  His 
arms  are  shorter  and  have 
more  freedom  of  motion  at 
the  wrist,  and  his  cranium 
is  better  balanced  at  the 
top  of  the  vertebral  column 
than   in  the   apes.     These 

Fig.    271.     The  framework    of    the    human  ff.„        o'rn^       cVinfflp^       dinner 
hand,     a  to /t.  carpal  bones;  /  to  J,  bones    ^^^&-       ^T^-f       i^IlUliie       aiOng, 

of  the  <^^^^g^^g^J°^^^g^^°"^^  °^  ^^^       using  the  arms  as  well    as 

the  legs  for  locomotion. 
The  chief  advantage  of  the  erect  attitude  is  that  it  sets 
the  hands  free  for  other  uses. 

The  human  hand  is  generalized  in  structure ;  its  skeleton 
is  very  like  that  of  the  foot  of  a  salamander  and  not  far 
removed  from  that  of  the  typical  vertebrate  (compare  figures 
271,  272  and  III).  It  is  much  like  the  ape's  hand  in  its 
opposable  thumb  and  its  freedom  of  rotation  at  the  wrist. 
These  two  features  make  it  adaptable  to  a  great  variety  of 
uses.  Its  readiness  at  grasping  and  turning  make  it  a 
splendid  servant  of  the  brain ;  for  it  can  be  used  in  exam- 
ining objects,  in  exploring  surfaces  and  in  moving  things 


RESPONSIVE  LIFE  OF  ORGANISMS  4S7 

about.  Thus  things  may  be  known  as  objects,  and  not  as 
mere  obtruding  features  of  the  general  environment.  It  is 
hardly  conceivable  that  the  specialized  hand  of  a  bird  or  of  a 
fish  could  be  of  much  use  in  the  educating  of  its  possessor; 
the  variety  of  sense  impressions  it  could  furnish  would  be 
very  limited.  Doubtless  the  possession  of  so  adaptable  a 
grasping  organ  has  been  a  large  factor  in  human  develop- 
ment. It  has  made  man  a  tool-using  animal.  It  is  the 
recognition  of  this  service  that  has  made 
hand-training  (manual  training)  an  integral 
part  of  our  educational  system. 

The  human  brain  is  distinguished  by  a 
very  great  development  of  the  cerebral  hemi- 
spheres.    These,  as  we  have  seen,  are  rela- 
tively small  in  the  salamander.     They  in-        \\lP'-'<i  y^ 
crease  in  size  with  improvement  in  mental  t^^^/f 

power  in  all  the  higher  vertebrates.  They  Qria'^ 
overspread  first  the  olfactory  and  then  the 
optic  lobes  and  the  upper  side  of  the  cere- 
bellum, and  in  the  higher  mammals  their 
cortex  becomes  thrown  into  folds  increasing 
thus  its  superficial  area.     They  reach  their  ^ 

^  -^  Fig.     272.     Bones   of 

maximum    development    in     the     human     the  foot  of  a  spotted 

salamander,     a,   fe- 

species,  exceeding   many    times  in   weip:ht     ^^^v   ^-   t'bia;    c. 

^  o  y  a  fibula;      d,      tarsal 

all  other  parts  of  the  nervous   system  put     bones;  e  phalanges, 
together. 

The  hemispheres  constitute,  as  we  have  seen,  the  chief  con- 
trol center  of  the  vertebrate  nervous  system.  This  added 
mass  of  nervous  matter,  which  was  not,  in  the  beginning  of 
development,  necessary  to  the  organism,  and  which  is  still 
unconcerned  with  the  ordinary  performance  of  the  most 
vital  processes  of  the  body  (although  connected  with  all), 
may  be  conceived  of  as  containing  innumerable  possible 
nerve  paths,  formed  by  the  association  together  of  its  ex- 


48S  GENERAL  BIOLOGY 

ceedingly  complicated  cell-arborisations.  In  them  are 
possible  channels  of  intercommunication  in  number  far  and 
away  beyond  the  needs  of  an  organism  for  the  performance  of 
the  acts  that  are  connected  with  the  inherited  instincts  of  the 
species.  The  potential  nerve  paths  of  the  brain,  are  at 
first  of  equal  resistance;  through  them  sense  perceptions 
may  find  their  way  and  responses  may  wear  their  channels 
until  all  the  main  highways  become  established  in  exper- 
rience. 

The  external  world  rains  down  its  innumerable  stimuli 
upon   the   organism.     Those    stimuli    that   are   related   to 

experience  have  the 
right  of  way,  and  de- 
termine action.  The 
experiences  that  ac- 
company action  'are 
retained  in  the  organ- 
ism to  augment  or 
modify  or  inhibit  fur- 
ther action.  Discrim- 
ination       between 

Fig.  273.     The  hand  of  a  Httle  girl.  stimuli  improves  with 

the  varying  of  experience.  Discernment  of  the  relation  be- 
tween cause  and  effect  follows,  and  this  may  determine  choice 
of  action ;  at  first  the  choice  is  based  on  the  expected  immedi- 
ate good  or  ill  results ;  later,  on  the  more  far-reaching  con- 
sequences of  the  act.     Morality  comes  in  here. 

In  both  body  and  brain  man  is  at  birth  far  more  poorly 
equipped  for  the  struggle  for  existence  than  any  other 
animal.  He  has  no  defensive  armor  to  w^ard  off  attacks  of 
enemies.  He  has  no  formidable  bodily  weapons,  teeth, 
fangs,  claws  or  horns,  to  make  them  fear  him.  He  has  no 
equipment  of  inherited  behavior  sufficient  to  insure  his 
safety.     His  new  born  spontaneity  of  movement  is  confined 


RESPONSIVE  LIFE  OF  ORGANISMS  489 

to  two  acts  both  of  which  are  directed  toward  self  preserva 
tion  and  not  toward  defense;  these  are  sucking  and  grasp- 
ing. He  has,  however,  a  brain,  that,  when  rightly  devel- 
oped, is  capable  of  supplying  all  these  deficiencies.  And 
he  has  a  long  period  of  infancy — far  longer  than  that  of  any 
other  animal — during  which  to  develop  it  .  Relieved  by 
parental  care  from  the  necessity  of  immediately  entering 
upon  the  struggle  for  existence,  he  has  time  to  learn,  to  feel 
and  to  do,  to  discriminate  and  to  act,  to  sift  and  to  try  an 
endless  variety  of  experiences  and  to  learn  both  wisdom  and 
discretion.  Infancy,  although  it  be  playtime,  is  in  man  and 
animals  alike,  a  time  of  preparation  for  the  serious  business 
of  life.     Play  is  but  practice  for  the  game  of  life. 

Language. — Man  is  the  only  animal  that  talks.  Birds 
chatter  and  sing;  insects  chirp  and  hum;  fiddler  crabs 
gesticulate,  and  dogs  have  many  ways,  familiar  to  ever)^  one, 
of  expressing  their  feelings;  and  the  rudiments  of  language 
are  doubtless  in  the  signs  and  calls  which  are  a  part  of  the 
social  habits  of  animals.  "Actions  speak  louder  than 
words."  By  many  sense  impressions  of  an  object  or  an  act 
man  may  gain  a  conception  of  its  qualities,  and  then  he  is 
able  to  conceive  of  the  qualities  severally,  and  apart  from 
the  thing  possessing  or  manifesting  them.  From  seeing 
swiftly  moving  objects,  he  may  conceive  of  swiftness  in  the 
abstract,  and  then  he  may  use  a  word  to  symbolize  that  con- 
ception. Whether  a  dog  or  any  other  animal  may  conceive 
of  swiftness  apart  from  a  swiftly  moving  object  seems 
highly  improbable. 

The  first  words  used  may  have  been  such  calls  to  com- 
panions as  two  persons  unacquainted  with  each  other's 
language,  might  today  agree  upon.  Or,  they  might  well 
have  been  vocal  signals  such  as  men  use  when  acting  in 
companies  to  secure  co-operation.  "All  together — hce-o!" 
is  such  a  combination  of  words  and  verbal  rudiments  as  we 


4QO  GENERAL  BIOLOGY 

often  hear  on  the  streets,  spoken  by  the  leader  of  a  group  of 
laborers.  The  efficiency  of  such  symbols  depends  upon  their 
being  understood;  there  must  be  general  acquiescence  in 
their  use. 

How  words,  as  condensed  and  convenient  symbols  of 
experience,  have  aided  mental  development  has  recently 
been  well  expressed  by  a  British  physiologist,  Professor 
Starling,  as  follows : 

"A  word  is  a  fairly  simple  motor  act,  and  produces  a 
correspondingly  simple  sensory  impression.  Every  word, 
however,  is  a  shorthand  expression  of  a  vast  sum  of  expe- 
rience, and  by  using  words  as  counters  it  becomes  possible 
to  increase  enormously  the  power  of  the  nervous  system  to 
deal  with  its  own  experience.  Education  now  involves  the 
learning  of  these  counters  and  of  their  significance  in  sense 
experience;  and  the  reactions  of  the  highest  animal,  man, 
are  for  the  most  part  carried  out  in  response  to  words,  and 
are  governed  by  past  education  of  the  experience-content 
involved  in  each  word." 

Without  language  one  may  profit  by  the  experience  of 
others  only  to  the  extent  that  he  is  an  observer  of  that 
experience;  but  experience  symbolized  in  words  may  be 
dissociated  from  the  individual  and  told  abroad. 

Tool  using. — Man  is  the  only  animal  that  uses  tools. 
Monkeys  will  throw  down  cocoanuts  from  trees  in  imitation 
of  or  response  to  stones  thrown  up  at  them:  and  a  little 
wasp  Ammophila  uses  a  pebble  held  by  her  jaws  to  pound 
down  the  soft  earth  over  her  completed  nest.  But  even  so 
simple  an  idea  as  the  using  of  a  club  for  defense  appears  not 
to  have  emerged  in  the  mind  of  any  animal.  Man,  however, 
had  both  more  need  to  supplement  his  weak  powers,  and 
more  range  for  adaptive  action  provided  in  the  accessory 
circuits  of  his  brain. 


RESPOXSIVE   LIFE   OF   ORGANISMS 


491 


d^ 


fk 


The  earliest  human  tools  were  very 
simple;  a  club,  a  flint  stone;  such  things 
as  might  be  selected  from  nature  already 
fitted  to  the  hand.  Better  tools  fol- 
lowed when  a  little  laljor  was  added  to 
their  preparation.  A  split  stick  lashed 
to  the  flint  gave  a  stone  ax;  and  split- 
ting and  sharpening  of  the  flint  yielded 
stone  knives.  A  great  variety  of  tools 
of  stone  and  wood  and  bone  and  horn 
followed;  and,  later,  tools  of  bronze  and 
of  iron.  Indeed,  the  kinds  of  tools  man- 
kind has  used  furnish  a  fair  index  of  the 
progress  of  the  race.  Cutting  tools  es- 
pecially have  been  made  the  basis  of 
ethnological  classifications. 

The  use  of  fire. — Man  is  the  only 
animal  that  uses  fire.  Many  animals 
undoubtedly  enjoy  the  glow  of  its 
warmth;  and  some  of  our  domesticated 
animals  appear  to  be  sensible  of  the  im- 
provement it  makes  in  the  cooking  of 
food.  But  no  animal  has  attained  to 
the  idea  of  adding  a  stick  of  wood  to  keep 
a  fire  burning. 

Fire  was  the  first 
of  nature's  resources 
to  be  pressed  into 
human  service.  Its 
use  appears  to  have 
been  known  to  all 
races  and  tribes  of 
mankind,  throughout  human  history.  It  served  prime- 
val man  in  many  ways.     It  increased  his  physical  comfort. 


VJ 


//  /• 


Fig.  274.  Primitive 
tools,  a  a  chipped  flint 
of  very  ancient  form. 
b,  c,  d,  flint  knives  of 
improved  design,  c.  a 
flint  arrow  head.  /,  a 
flint  spear  head  g,  a 
bone  fish  hook.  /;,  /, 
bone  needles.  ;.  a 
wooden  bowl  k,  a 
wooden  comb.  /.  a 
necklace  of  teeth  and 
claws. 


f 


492  GENERAL  BIOLOGY 

It  bettered  his  rough  food.  It  warded  off  the  beasts  by  night. 
It  aided  in  the  preparation  of  his  crude  tools — the  shaping 
of  his  club  and  spear,  the  splitting  of  his  flints,  etc. 
It  hollowed  the  log  that  was  thereby  transformed  into  a 
canoe — his  first  conveyance. 

The  physical  comfort  of  the  fireside  glow  man 
shares  with  his  animal  friends;  he  differs  from  them  in  the 
foresight  that  anticipates  future  needs,  and  provides  the 
means  to  gratify  them.  Even  with  all  our  modern  im- 
provements in  heating  appliances  we  cling  to  the  open  blaze 
with  a  love  that  is  bom  of  primeval  experience. 

The  use  of  fire  for  cooking  may  have  been  first  learned 
by  the  accidental  discovery  of  the  greater  palatability  of 
flesh  or  of  tubers  that  had  been  roasted  in  wild  fires.  Doubt- 
less the  earliest  modes  of  cooking  were  roasting  over  the 
open  fire  and  roasting  in  hot  ashes.  Water  was  first  heated 
for  the  boiling  of  food  by  the  addition  of  hot  stones  to  the 
vessels  containing  it;  it  is  still  so  heated  by  certain  North 
American  Indians.  The  earliest  water  vessels  were  shells, 
as  of  cocoanut  or  gourd,  and  the  crania  of  vanquished  ene- 
mies; and  the  boiling  of  food  over  a  fire  had  to  wait  on  the 
invention  of  fire-proof  vessels.  The  first  of  these  were 
earthen  vessels,  which  were  later  succeeded  by  pots  of 
bronze  and  of  iron. 

2.     Unwritten  human  history 

The  sources  of  cur  knowledge  of  the  evolution  of  the 
human  species  are  the  three  "great  historical  documents" 
already  familiar;  palaeontology,  phylogeny  and  ontog- 
eny; but  for  these  as  applied  to  man  there  are  special 
names  to  be  used.  There  is  in  the  case  of  men  and 
animals  an  actual  record  of  the  past,  incomplete  but  indis- 
putable. It  is  preserved  in  the  bones  and  teeth  and  armor 
of  animals  and  its  study  is  known  as  palaeontology.     It  is 


RESPONSIVE  LIFE  OF  ORGANISMS  493 

preserved  in  the  weapons  and  defenses  that  man  has  sub- 
stituted for  fangs  and  claws  and  armor,  and  in  the  imperish- 
able products  of  his  hands,  and  its  study  is  known  as 
archaeology.  There  is  also  the  same  opportunity  for  com- 
parative study  of  developmental  attainments  in  men  and 
animals,  and  for  arranging  genetic  series  and  deducing  his- 
tory therefrom;  for  different  races  of  men  exist  in  very 
different  cultural  stages.  The  study  of  these  is  called 
ethnology.  The  development  of  the  individual  is  of  some 
historical  value  also  even  here,  for  the  corroborative  evi- 
dence that  it  ma}?^  furnish. 

Archaeology. — AVritten  history  goes  back  but  a  few 
thousand  years,  but  the  records  of  archaeology  extend  back 
hundreds  of  thousands  of  years  further.  The  oldest  exten- 
sive series  of  human  remains  have  been  found  in  the  inter- 
glacial  deposits  of  the  ice  age.  These  consist  of  man's  own 
skeleton,  his  tools  and  the  charred  remnants  and  ashes  from 
his  fires.  They  are  found  mainly  in  caves,  associated  with 
the  bones  of  cave-dwelling  animals.  The  extinct  cave 
bear  and  the  mammoth  were  his  contemporaries,  the  former 
being  his  competitor  for  such  shelter  as  caves  afforded.  His 
tools  at  this  period  were  few,  and  of  the  simplest  sort; 
chipped  flints,  a  club,  a  sharpened  bone,  etc. 

The  objects  of  his  home  environment  were  such  as  be- 
strew the  lair  of  the  wild  beast  in  similar  situations — chiefly 
the  remains  of  his  feasts,  the  most  imperishable  things 
being  the  bones  of  his  victims.  Among  these  arc  found 
human  bones,  split  ingeniously  for  the  ready  extraction  of 
the  marrow — a  choice  morsel  of  his  diet.  It  is  not  an  attrac- 
tive picture  of  the  life  he  lived  that  these  facts  suggest.  It 
differed  from  that  of  the  cave  dwelling  beasts  chiefly  in  the 
use  he  made  of  tools  and  of  fire.  There  is  a  faint  promise  of 
his  later  attainments  in  the  marks  of  scanty  workmanship 
found  upon  his  tools. 


494 


GENERAL  BIOLOGY 


We  can  not  go  into  the  fascinating  story  that  is  written 
in  the  remains  of  later  date;  the  sHght  changes  of  his 
skeleton,  and  increase  of  cranial  capacity ;  the  improvement 
and  diversification  of  his  tools  of  flint  and  wood  and  bone 
during  the  Age  of  Stone  (when  the  use  of  metals  was  as  yet 
unknown) ;  the  development  of  implements,  and  of  articles 
for  personal  adornment,  and  the  beginnings  of  art;  the  vast 
changes  in  his  material  equipment  during  the  succeeding 
ages  of  bronze  and  of  iron.  No  written  account  of  these 
records  of  human  progress  can  be  equal  in  value  to  a  thought- 
ful visit  to  any  good  museum  of  antiquities,  in  which  the 
archaeological  exhibits  are  arranged  in  evolutionary  se- 
quence. The  cruder  materials  with  which  archaeology 
deals,  although  much  neglected  in  the  past,  have  come  to  be 
appreciated  as  among  the  rarest  of  human  treasures. 

Ethnology. — As  amoebas  continue  to  exist  on  the  earth 
along  with  men,  so  savagery  and  all  intermediate  conditions 
persist,  along  with  the  most  modern  types  of  civilization. 
And  as  the  primitive  forms  of  life  are  restricted  to  the  places 
that  are  left  unoccupied  by  the  dominant  types,  so  the  more 


Fig.  275.     Man. 


RESPONSIVE  LIFE  OF  ORGANISMS  495 

primitive  types  of  culture  are  relegated  to  the  out-of-the- 
way  places  of  the  earth.  Comparative  ethnology,  therefore, 
has  had  the  same  kind  of  opportunities  as  comparative 
anatomy,  and  has  made  use  of  them  with  similar  results; 
i.  e.,  cultural  types  have  been  described  and  classified. 
Similarly,  also,  the  different  systems  of  classification  have 
not  always  been  in  agreement.  A  simple  grouping  based 
on  the  main  features  of  man's  methods  of  getting  a  living 
from  the  earth,  will  answer  our  present  purpose.  It  recog- 
nizes four  principal  stages  in  human  progress:  i)  the 
hunter  stage;  2)  the  shepherd  stage;  3)  the  artisan  stage, 
and  4)  the  inventor  stage. 

The  earliest  of  these  is  the  hunter  stage.  It  comprises 
that  long  period  during  which  primitive  man  lived 
upon  the  products  of  nature,  lived  as  a  freebooter,  picking 
from  the  wild,  cultivating  nothing  for  food.  He  was  less 
provident  than  the  squirrel  or  the  ant,  and  far  less  indus- 
trious. He  was  satisfied  when  present  needs  were  met,  and 
accumulated  nothing.  He  built  only  the  rudest  shelter,  at 
the  first  wore  no  clothing,  and  had  no  society.  His  food  was 
doubtless  not  very  different  from  that  of  the  cave  bear,  with 
which  he  was  a  competitor;  the  flesh  of  animals  and  the 
fruits  and  roots  of  plants;  perhaps,  also,  with  an  occasional 
feast  of  wild  honey.  His  early  home  was  by  the  waterside, 
and  fish  were  a  most  dependable  part  of  his  living.  Fish  he 
could  catch  by  hand,  or,  better,  with  a  bone  hook,  or  with  a 

spear.     It  was  easier  to  spear 
^  ^    W  i^  ^^^  from  a  floating  log,  and  a 

ZZ-Jij\' __^1 hollowed  log  with  a  pole  for 

propulsion   was   probably   his 
Fig.  276.    Co-operation.  earliest    Conveyance.     Larger 

canoes  demanded  more  hands  to  propel  them:  and  in 
the  propelling  of  these,  and  in  the  driving  of  the  fish  upon 
the  shoals  may  have  begun  cooperative  labor.    Cereal  grains, 


496 


GENERAL  BIOLOGY 


especially  rice  and  barley,  early  became  important  food 
stuffs,  and  with  the  stone  mortar  for  grinding  grains  house- 
hold arts  may  be  said  to  have  begun. 

The  pastoral  stage  is  ushered  in  with  the  beginning  of  the 
domestication   of  animals   and   the   cultivation   of   plants. 
When  man  tamed  the  wild  things,  some  of  them  rewarded 
his  care  by  furnishing  him  with  a  larger  and  more  depend- 
able food  supply.     Thus 
foresight  grew,  and  agri- 
culture began.     The  pos- 
session   of      fields    and 
folds    made    for   settled 
homes    and    for    social 
organization.    An  abun- 
dant food  supply  could 
support  a  larger  popula- 
tion.        The   history   of 
nations      begins       here. 
The    first  agricultural 
implements  were   crude 
The  first  mill 


Fig.    277. 

(California    Indians),     b,     a 

split  wood  handle,     c,  a  wooden  shuttle. 

a  wooden  plow. 


a    bow 


Primitive    implements,      a,     a,    u^ww  , 

stone    ax,   with  CUOUgh 


d. 


was  a  stone  mortar;  the 
first  plow  was  a  crooked  stick,  the  first  apparatus  for  weaving 
of  fibres  or  hair  into  cloth  was  a  wooden  shuttle.  With  bet- 
ter food  supply,  less  time  was  required  for  obtaining  a  liveli- 
hood and  the  energies  thus  set  free  were  available  in  some 
measure  to  be  devoted  to  the  perfecting  of  the  finish  of 
manufactured  products  and  the  development  of  the  fine 
arts. 

The  artisan  stage  naturally  followed  upon  the  develop- 
ment of  increased  food  supplies;  for  exchange  of  products 
began,  and  commerce  demanded  wheels  and  keels.  Im- 
proved tools  of  metal  were  needed,  and  artisans,  of  various 
sorts,  to  use  them.     Money  came  to  be  used  as  a  medium  of 


'   RESPONSIVE  LIFE  OF  ORGANISMS  497 

exchange,  replacing  the  barter  of  products  that  was  charac- 
teristic of  the  pastoral  stage.  Men  began  to  gather  into 
cities.  In  preceding  stages  all  men  were  engaged  in  much 
the  same  pursuits,  but  now  they  differentiated,  one  man 
producing  articles  for  the  use  of  the  others,  and  receiving 
the  products  of  the  others  in  exchange. 

Finally,  came  the  inventor  stage.  The  forces  of  nature  were 
harnessed  to  do  men's  work.  Artisans  largely  gave  place  to 
operators  of  machines.  Production  was  vastly  increased; 
population  grew  apace.  The  exigencies  of  commerce  de- 
mand the  centralization  of  lines  of  communication  and  of 
transportation  and  thus  cities  grow.  And  the  end  of  this  is 
not  yet. 

Doubtless  the  earliest  of  these  periods  was  most  extensive; 
the  night  of  savagery  was  long  and  the  dawn  broke  slowly. 
But  it  was  a  period  of  physical  perfecting  and  of  sound 
beginnings  of  mental  improvement.  During  the  long 
struggle  with  animals,  better  equipped  by  nature  for  fight- 
ing, man  had  to  match  their  strength  and  cunning  with  his 
wit.  Thus  he  gained  good  eyes  and  ears,  a  supple  frame, 
quick  muscles  and  strong  sinews,  hands  that  could  control 
weapons  with  deftness  and  precision,  and  above  all,  a  brain 
that  could  turn  to  advantage  the  circumstances  of  his  en- 
vironment. The  elimination  of  the  unfit  was  then  most 
rigorous.  The  savages  of  all  dominant  tribes  are  fine 
physical  specimens,  and  it  is  not  too  much  to  say  that  on 
this  basis  of  physical  fitness  all  subsequent  history  is  built. 
The  foresight  that  would  put  a  stick  of  wood  on  a  fire  to  keep 
it  going,  that  would  shape  a  stone  for  hitting,  or  that  would 
improve  its  efficiency  by  the  addition  of  a  handle,  marked  an 
enormous  psychological  departure  from  the  status  of  the 
brute.  The  native  taste  that  shaped  an  arrow  heail  witli 
symmetry  and  beauty,  or  that  traced  with  flint  its  crude 
fancy  in  a  picture  on  bone,  had  in  it  the  germ  of  art.  Given 
these,  all    language,  all    subsequent  history  was  possible. 


498 


GENERAL  BIOLOGY 


Ontogeny. — From  birth  onward  the  developmental 
phases  in  man  do  not  help  greatly  with  the  unravelling  of 
his  history,  for  they  are  much  altered  by  environmental 
influences.  But  there  are  many  things  that  are  suggestive 
of  a  sort  of  correspondence  Avith  phylogeny.  The  infant  is 
bom  with  hands  that  are  fitted  for  grasping,  and  capable  of 
sustaining  his  weight.  When  he  begins  to  travel  he  goes  on 
"all  fours,"  and  it  is  not  until  he  assumes  the  erect  position 


n 


Fig  278.  The  beginnings  of  the  arts.  I,  a  carved  dagger  made  from  a  human 
bone  k.  a  stringed  mstrument  (Upper  Nile).  /.  an  instrument  to  be  used 
against  evil  spirits  (S.  Australia),  ni  a  bronze  fish  hook  (Lake-dwellers  of 
Switzerland)  m,  an  instrument  for  correcting  heterodox  opinion,  (known  as  a 
"spiked  roller":  the  infidel  was  usually  stretched  naked  upon  a  rack  and 
rolled  vigorously  with  this  instrument  as  a  means  of  correcting  his  beliefs: 
Germany    Middle  Ages).     (All  after  Brinton). 

on  his  feet  that  he  advances  in  action  beyond  his  four-footed 
relatives.  Relieved  of  the  function  of  support,  his  arms 
learn  throwing  and  striking  and  pulling.  He  imitates  all 
sorts  of  movements,  and  engages  endlessly  in  play  that  is 
imitative  of  the  work  of  his  elders,  and  that  is  essentially  like 
the  play  of  other  young  mammals.  At  about  the  age  of 
twelve  he  appears  to  arrive  at  consciousness  that  he  is  a 
part  of  a  community;  for  he  begins  to  play  with  his  fellows 
at  cooperative  games  and  organized  sports;  he  enters  upon 
team  work. 


RESPONSIVE  LIFE  OF  ORGANISMS 


499 


Ethnic  culture  stages  are  rapidly  passed  through  in  the 
experience  of  his  earliest  years.  At  the  beginning  he  is  a 
freebooter,  taking  what  he  likes  of  what  he  sees,  recognizing 
no  rights  of  property,  and  doing  nothing  to  produce  what  he 
consumes.  Then  he  enters  upon  the  domestication  of  ani- 
mals and  the  cultivation  of  plants  quite  naturally  and  on 
his  own  account.  He  cultivates  the  good  will  of  his  pets  and 
feeds  them,  and  makes  them  work  for  him.  lie  plants 
flowers  and  vegetables  and  clearly  recognizes  ownershij^  in 
these  things.  Then  he  comes  to  be  interested  most  keenly 
in  tools  and  in  the  things  he  can  make  with  them.  At  this 
age  he  is  vastly  more  benefited  by  the  gift  of  a  jack  knife  or  a 
hammer  than  of  more  complicated  toys.  An  Indian's  bow 
and  arrow  is  more  to  be  desired  than  a  repeating  shot  gun. 
But  soon  he  will  aspire  to  have  the  complicated  toys  and 
the  engines  and  the  hand  organs.  The  inventor  stage  is 
upon  him  even  before  he  is  entered  in  school. 


Fig.  279.     Play  is  preparation  for  business 


500 


GENERAL  BIOLOGY 


J.     The  social  organism. 

Human  history  begins  in  isolation  and  not  in  society. 
Primitive  man  was  a  barbarian,  and  the  hfe  of  a  barbarian 
is  essentially  solitary.  Probably  he  made  a  friend  of  his 
dog  earlier  than  of  any  person  outside  his  own  household; 
for  strangers  were  enemies.  And  the  reason  for  this  is  not 
far  to  seek.  He  must  have  room,  or  starve.  He  could  not 
live  on  grass  or  any  other  plant  product  of  unlimited  abun- 
dance, as  do  the  m.ammals,  that  nature  had  made  gregarious 


■■•*«^'' 


Fig.  280.      Typical  gregarious  herbivores. 

(fig.  280);  nor  had  he  superior  powers  of  locomotion  that 
would  enable  him  to  get  about  and  find  widely  scattered 
food  products  as  do  the  social  birds.  The  households  of 
cave-dwellers  were  therefore,  few  and  far  between*. 

Nor  are  the  habits  of  a  barbarian  favorable  to  social  life. 
He  eats  like  an  animal  when  hungry,  and  waits  until  hungry 


*Ethnologists  estimate  that  without  any  agriculture,  it  requires 
sixteen  square  miles  of  territory  in  temperate  regions  to  furnish 
sufficient  available  food  for  one  person. 


RESPONSIVE   LIFE  OF  ORGANISMS  501 

again  before  setting  out  to  find  more  food.  He  is  quarrel- 
some when  hungry  and  lazy  when  fed,  and,  being  perfectly 
satisfied  with  himself,  lacks  the  main  spring  of  progress. 
The  narrow  sympathy  that  in  primitive  man  was  bom  of  his 
parental  and  conjugal  instincts,  and  that  was  limited  to  his 
family,  may  have  been  widened  through  his  dealings  with 
animals  when  he  had  domesticated  them.  The  man  who 
will  bind  up  the  broken  leg  of  his  dog,  or  pull  his  ox  out  of  a 
ditch  is  more  likely  to  help  his  fellow  man  when  found  in  dis- 
tress. Tolerance  of  fellow  men  led  to  the  formation  of 
tribes,  which  at  first  were  composed  of  a  few  allied  families. 
Primitive  tribes  retain  the  characters  of  the  individual  bar- 
barian; they  kill  outsiders,  and  often  eat  them,  and  not  in- 
frequently they  similarly  dispose  of  a  part  of  their  own 
female  infants,  in  order  to  keep  the  birth-rate  down;  the 
tribe,  also,  must  have  room.  Tribal  societies  are  ever  at 
war;  and  wars,  besides  preventing  increase,  block  progress, 
destroy  property,  and  curtail  desire  to  do  or  to  build.  The 
beasts  were  man's  first  enemies,  but  since  he  learned  to 
make  efficient  fighting  weapons,  his  own  kind  have  been  his 
worst  enemies. 

The  growth  of  nations  may 
be  said  to  begin  with  the  culti- 
vation of  plants  in  fields.  This 
made  for  settled  homes,  for  the 
establishment  of  property 
rights,  and  of  law  and  order 
(within  narrow  limits),  for  the 

Fig.  281.     Threshing   scene.     From    a  development  of  knowledge,  and 
painting    on    the  wall  of    an   ancient   j-  .  i  i       •  /■      , 

Egyptian  tomb  (after  Brinton).  lOr    the  aCCUmmulatlOU   OI    the 

meansof  livelihood  that  should 
set  men's  hands  free  to  do  something  besides  meeting  the 
needs  of  the  hour,  and  their  minds  free  to  forecast  future 
needs.     Unfortunately  these  needs  were  too  largely  needs 


502  GENERAL  BIOLOGY 

of  defence  against  other  nations.  For,  in  the  beginning  the 
savage  characteristics  of  their  constituent  tribes  were 
passed  on  to  the  new  formed  nation.  Nations  initiate  wars  to 
annihilate  other  nations.  Most  of  the  migrations  of  the 
human  race  have  been  migrations  of  conquest.  Hence,  the 
earUer  civihzations  of  the  earth  could  onl}^  grow  where  a 
nation  could  exist  in  comparative  isolation.  Such  places 
were  the  desert-bordered  valley  of  the  Nile  in  Egypt,  the 
mountain-fringed  table  lands  of  Mexico  and  Peru,  etc. 
They  did  not  grow  in  the  earth's  exposed  areas,  such  as  the 
Mississippi  Valley,  although  the  works  of  the  mound-build- 
ers show  that  great  constructive  efforts  once  started  there. 
There  was  security  only  in  isolation  until  the  growth  of  a 
broader  sympathy  and  the  dawn  of  a  miore  constructive 
social  spirit. 

Socially,  primitive  man  was  unspecialized.  Aside  from 
differences  of  the  sexes,  there  was  nothing  preformed  in  his 
bodily  organization  determining  what  should  be  his  rela- 
tions to  other  individuals  of  his  kind.  There  was  no  pre- 
formed division  of  labor  as  in  bees;  there  were  no  castes,  as 
in  the  ants  and  the  termites.  He  came  into  possession  of  no 
particular  modes  of  social  activity  by  inheritance.  If  he 
attained  to  social  co-operation  he  had  to  acquire  it  for  him- 
self. But  he  possessed  speech;  and  speech  wondrously 
facilitated  cooperation  and  the  exchange  of  experience  and 
the  comparison  of  old  ways  and  the  development  of  new 
ones,  and  conditioned  further  development.  And  he  pos- 
sessed laughter — a  fountain  of  social  responsiveness,  and  a 
means  of  extending  sympathy  and  developing  comradeship 
surpassing  speech.  And  the  primary  demand  of  social 
progress  is  sympathy,  and  good  will  toward  men. 

Animism.  Animals  live  in  a  world  of  sense  perception, 
but  man  has  always  lived  to  a  greater  or  less  extent,  in  a 
super-sensual  world — a  world  of  ideas.     In  language  man 


RESPONSIVE  LIFE  OF  ORGANISMS 


503 


Fig.  282.     Social  co-ordination. 

crystallized  his  concepts  and  gave  them  currency.  They 
were  concepts  first  of  the  things  he  saw  and  then  of  their 
properties;  also,  of  the  things  he  imagined,  and  then  of  their 
imagined  properties.  Having  attained  to  a  discernment  of 
the  relation  between  cause  and  effect,  his  mind  demanded 
explanations  of  the  things  in  the  world.  Any  explanations 
were  better  than  none.  When  he  had  gained  ascendency 
over  the  powers  of  the  animal  world  and,  by  the  establish- 
ment of  the  rudiments  of  agriculture  and  household  arts, 
had  foref ended  himself  against  immediate  want,  he  took 
to  thinking:  the  great  problems  of  birth  and  death,  of 
times  and  seasons,  and  of  the  heaven  and  the  earth  were 
before  him. 

He  was  interested  in  the  relation  between  his  own  body 
and  the  breath  or  spirit  that  animates  it;  and  out  of  the 
consideration  of  this  problem,  he  evolved  ideas  that,  more 
than  any  other,  have  dominated  all  the  intratribal  social 
intercourse  of  subsequent  history.  He  conceived  of  a  spirit 
of  like  form  with  the  body  but  impalpable  and  separable 
from  the  body,  that  goes  a-wandering  from  it  in  dreams  and 
trances,  but  returns  again;  and  that  leaves  the  body  at 
death  to  wander  elsewhere  as  a  disembodied  spirit,  or  to 
take  up  a  new  abode.  He  conceived  that  animals  also 
possess  kindred  spirits  and  he  wore  the  teeth  and  claws  of 


Fig.  283.     General  sociability. 


504  GENERAL  BIOLOGY 

ferocious  beasts  in  the  belief  that  thus  he  assumed  their 
powers.  His  imagination  peopled  the  world  with  spirits; 
mostly  evil  ones,  with  fearful  powers  for  harm,  demanding 
to  be  propitiated  by  sacrifices,  offerings  or  worship,  or  con- 
trolled by  magic.  These  spirits  might  enter  into  human  bodies, 
producing  demoniacal  possession,  witchcraft,  disease,  or 
death.  This,  in  brief,  is  animism.  It  appears  to  have  been 
the  earliest  form  of  both  philosophy  and  religion  of  all 
savage  tribes.  It  has  practically  no  moral  purpose  or 
effect.  It  appeals  mainly  to  men's  fears;  for  although  it 
peoples  the  world  with  both  good  and  evil  spirits,  the  evil 
ones  are  mainly  worshipped,  because  fear  is  a  more  powerful 
emotion  than  reverence. 

Some  of  the  specialized  manifestations  of  animism  are, 
i)  Spiritism,  the  belief  in  the  existence  of  free  spirits: 
ghosts,  etc.  2)  Fetichism,  the  belief  that  the  spirit  resides 
in  an  object,  which  then  becomes  a  fetish,  and  is  treasured 
for  the  magic  power  it  possesses;  charms,  etc.,  such  as  the 
rabbit's  foot,  the  old  horse-shoe,  and  the  four-leaved  clover. 
3)  Magic,  the  belief  that  the  spirit  is  controlled  (or  that  some 
supernatural  result  is  wrought)  through  the  performance  of 
some  act.  4)  Ancestor  worship,  the  belief  in  the  presence 
and  supernatural  power  of  the  good  spirits  of  dead  ancestors, 
etc.  A  little  study  of  the  harmless  survivals  (psychic  ves- 
tigial relicta)  of  these  things  should  be  convincing  that 
animism  has  left  its  permanent  records  with  us,  and  that 
these  records  are  of  interest  and  value  as  landmarks  of 
an  evolving  culture. 

Study  64.     The  survivals  of  animism  in  our  own  times. 

The  materials  for  this  study  will  be  furnished  out  of  our 
experience,  and  out  of  the  behavior  of  the  people  we  have 
known.  Illustrations  of  fetishism  and  of  magic  will  be  most 
available.     A  dozen  or  more  examples  of  each   of  these 


RESPONSIVE  LIFE   OF  ORGANISMS 


505 


should  be  subject  to  recall  in  the  memory  of  any  observant 
person.  Perhaps  a  comparative  statement  will  bring  into 
relief  their  main  characters.  The  following  form  is  suggested : 


FETISHES. 

Potency 
resident  in  what 

Conditions  of 
its  efficiency 

Effects 

Attendant 
manifestations 

Ex.,  a  mad  stone 

laid  upon  the 
wound  caused 
by  mad  dog 

cures 
rabies 

sticks  a    longer  or 
shorter  time  to  the 
flesh,  according  to 
the  extent   of   the 
evil  influence  to  be 
overcome. 

MAGIC, 


The  act 


Ex.,    crow- 
ing of  a  cock 


Conditions 


at  the  front 
door  in  the 
morning 


Effects 


will  bring  com- 


Belief  of  what 
people 


Scotch, 


pany  during!   English,  etc. 
the  day 


Nowadays  we  hold  magic  and  charms  in  so  light  esteem, 
that  we  are  apt  to  overlook  the  tremendous  importance  they 
have  had  in  the  past.  Our  language  and  literature  and  his- 
tory are  full  of  them.  Our  clothing  drips  with  them,  for  it 
grew  out  of  them.  Is  there  not  a  place  for  a  charm  on  a 
watch  chain?  and  what  is  a  locket  but  a  case  for  ^ome  sweet 
magical  thing  like  a  lock  of  hair,  that  may  be  worn  next  the 
believer's  palpitating  heart?  Betimes,  we  lay  aside  our 
seriousness  and  have  a  little  romp  of  childhood  in  this  intel- 
lectual haymow  of  stored  primeval  experiences.  Especially 
do  we  this  at  holiday  seasons,  when  the  emotions  rule  and 
when  dormant  racial  instincts  waken  easily.  We  hang  the 
mistletoe  at  Christmas  tide,  and  at  Hallow-e'en  we  inilulge 


5o6  GENERAL  BIOLOGY 

in  all  sorts  of  absurd  divinations.  We  tell  fortunes.  We 
consider  signs.  We  give  birthstones.  We  tell  ghost  stories 
in  the  dark — the  primeval  setting,  and  the  condition  that 
stimulates  the  latent  racial  emotions  which  we  wish  to  recall 
in  diluted  and  enjoyable  form. 

But  these  are  matters  serious  enough  to  many  of  our  own 
population;  witness  the  advertising  columns  of  the  necro- 
mancers and  magicians  in  any  of  the  Sunday  newspapers. 
And  we  do  well  not  to  forget  with  what  tyranny  such  ideas 
have  held  sway  over  our  entire  race  during  most  of  its  his- 
tory. Selfish  and  vainglorious  magicians  and  sorcerers  and 
healers  have  been  able,  through  appeals  to  fear,  to  practice 
great  oppression,  and  to  add  a  grievous  burden  to  the  sins 
and  miseries  of  all  savage  peoples.  The  earliest  records  of 
all  races  are  full  of  this.  Happily,  they  tell  also  of  prophets 
and  seers  who  have  risen  to  point  out  truer  relations  between 
cause  and  effect,  and  of  great  leaders  who  have  sought  to 
free  men  from  the  bondage  of  superstition,  and  of  teachers 
who  have  labored  to  dispel  ignorance — its  cause. 

Besides  wars  and  superstitions,  there  are  yet  other  trou- 
bles of  his  own  creation  that  have  vexed  man  throughout  his 
history.  He  has  never  been  satisfied  with  food,  but  has 
always  and  everywhere  wanted  something  added  to  his  diet 
to  excite  or  modify  the  action  of  his  nervous  system. 
Opium  and  alcohol  are  typical  of  these;  and  the  use  of 
stimulants  and  narcotics  has  added  and  is  still  adding 
enormously  to  the  vast  sum  of  human  misery  in  all  nations. 

Nor  has  he  ever  anywhere  been  clothed  with  the  utmost 
possible  comfort  and  convenience.  Dress  was  originally 
for  charm  bearing,  for  ornamentation,  or  for  sign  of  rank  or 
station;  and  it  is  little  modified  from  its  traditional  func- 
tions by  considerations  of  comfort.  Every  improvement  in 
methods  of  getting  a  livelihood  that  has  set  men's  hands 
free  from  constant  toil  and  given  time  for  thought,   has 


RESPONSIVE  LIFE  OF  ORGANISMS  507 

made  opportunity  also  for  the  growth  of  social  habits  with- 
out thought.  In  the  social  organism ,  as  well  as  in  the  physical, 
things  have  run  their  course  unchecked  by  environing 
conditions.  Traditions  are  usually  cherished  quite  irrespec- 
tive of  their  usefulness. 


Fig.  284.     A  stylish  young  Botocudo  Indian  (Brazil).   Psychological    orthogenesis. 

(After  Brinton). 

Social  integration. — Society  is  first  an  aggregate  and 
afterwards  an  integrate  of  human  beings.  The  social  or- 
ganism has  followed  the  same  developmental  methods  that 
have  perfected  the  multi-cellular  body,  and  made  of  it 
an  integrate  organism.  Ancient  history  is  filled  with  end- 
less experiments  at  social  integration.  The  parts  brought 
together  at  first  lacked  the  essential  bond  of  mutual  de- 
pendence. They  were  alike  save  for  the  differentiation  of 
the  sexes,  and  each  man,  or  at  least  each  family,  was 
capable  of  getting  along  alone.  Differentiation  and  divis- 
ion of  labor  was  necessary  here  as  in  the  physical  organisms 
to  create  the  need  of  one  part  for  the  complemental  parts 
that    should    bind    all    indissolubly    together. 


5o8  GENERAL  BIOLOGY 

Differentiation  occurred  in  strict  accordance  with  the 
physical  needs  of  men,  which  are  the  same  as  those  of  ani- 
mals— needs  of  food  and  shelter  and  defense  against  enemies. 
Hence  the  earliest  of  callings  are  those  of  hunter  and  fisher- 
men, soldier  and  scout,  shepherd  and  husbandman,  build- 
er and  weaver,  etc.  Precise  fitness  of  any  of  these  callings 
involved  loss  of  fitness  for  the  others,  and  made  the  special- 
ist in  one  more  or  less  dependent  on  all  the  others  for  that 
part  of  his  living  that  he  could  not  so  well  provide  for  him- 
self. The  primary  condition  of  social  integration  is  mutual 
dependence. 

Social  stability  demands  coordination.  The  parts 
must  function  harmoniously,  so  that  the  actions  of  any 
or  of  all  shall  be  made  subservient  to  the  welfare  of  all. 
This  demands  i)  intercommunication  between  parts,  and  2) 
the  development  of  centers  of  control.  Intercommunica- 
tion is  primarily  needed  for  exchange  of  products.  There- 
fore, as  the  physical  organism  develops  circulatory  appara- 
tus, so  the  social  organism  develops  channels  of  trade.  Are 
they  not  popularly  characterized  as  "arteries  of  commerce"  ? 
Means  of  sensory  communication  are  next  needed ;  and  as  the 
physical  organism  develops  nerves  so  the  social  organisms 
develops  postal  and  telegraphic  lines.  And  do  we  not  hear 
these  fitly  spoken  of  as  "nerves  of  intelligence"?  Control 
centers  in  the  physical  organism  arise,  as  we  have  seen,  where 
nerve  cells  are  gathered  together  to  form  ganglia;  and 
similarly  in  a  nation  they  develop  just  as  naturally  wherever 
those  individuals  live  who  assume  the  function  of  coor- 
dinating and  directing  the  activities  of  the  whole  body  poli- 
tic, (councils,  directorates,  congresses  etc.).  And  are  not 
these  also  with  some  propriety  often  called  "centers  of 
trade,  of  culture,  or  of  government"? 

When  organization  has  proceeded  to  the  point  of  establish- 
ing control  centers  its  efficiency  depends  on  the  concurrent 


RESPONSIVE  LIFE  OF  ORGANISMS  509 

development  of  such  organs  of  outlook  as  are  capable  of 
giving  knowledge  of  the  outside  world,  and  the  maintenance 
of  such  mutual  responsiveness  and  adaptability  of  parts 
within  as  will  admit  appropriate  actions  in  response  to 
the  things  discerned.  The  watchman  in  the  tower  is  as  the 
eye  of  primitive  society;  and  equally  so  are  the  explorer  and 
the  investigator  in  later  times.  As  the  body  is  profited  by 
its  distance  receptors,  so  society  is  profited  by  its  seers  and 
prophets  of  truth.  It  is  natural,  therefore,  that  with  later 
specialization,  groups  of  individuals  should  have  been  set 
apart  from  the  ordinary  avocations  to  serve  society  as 
watchmen,  devoting  their  energies  to  scanning  the  face  of 
nature  and  to  the  discovery  of  the  principles  of  science. 
The  scientific  centers  are  as  the  eyes  of  a  nation. 

But  eyes  are  merely  receptors;  the  effectors  or  rulers  are 
elsewhere  in  the  body.  Given  good  eyes,  fitness  of  reaction 
yet  depends  on  the  discriminative  powers  and  the  capacity 
for  correct  coordinated  responsiveness  of  the  organism  as  a 
whole.  It  is  possible  that  the  worst  of  actions  may  follow 
upon  the  best  of  vision.  Society  is  not  bound  to  progress. 
It  may  go  forward,  or  it  may  halt,  like  a  salamander  that 
stands  blinking  at  the  light,  and  then  runs  back  to  its  hole. 
So  in  our  own  time  it  seems  to  be  blinking  at  the  question  of 
international  peace. 

Society  makes  progress  as  its  constituent  units  become 
clear  in  perception  united  and  correct  in  discrimination  and 
inference,  and  concordant  in  action.  The  parts  must  not 
only  act  together  (harmony  is  not  all  that  is  necessary) ; 
they  must  act  together  in  profitable  ways. 

Social  conduct.  The  individual  begins  life  as  a  single 
cell,  and  has  first  of  all  to  run  over  in  ontogeny  a  course  in 
phylogenetic  history  that  is  enormously  long.  This,  how- 
ever, is  quickly  passed.  A  sound  body  and  well  organized 
animal  instincts  are  his  by  right  of  birth.      He  has  yet  to 


5IO  GENERAL  BIOLOGY 

retrace  the  course  of  human  development ;  and  this  though 
comparatively  short,  is  beset  with  difficulties;  for  his  art 
and  science  he  must  for  himself  acquire.  Nature  will  make 
of  him  only  a  barbarian;  nurture  must  make  of  him  a 
citizen. 

He  must  first  of  all  acquire  the  methods  of  education. 
He  begins  with  trial  and  error;  but  this  method  is  too  slow, 
too  uncertain  in  its  results,  and  too  apt  to  cultivate  ways  of 
going  elaborately  wrong,  alongside  of  those  which  go  right. 
He  must  learn  to  imitate,  and  must  learn  by  imitiation.  He 
must  learn  to  do,  or  not  to  do,  as  others  do.  By  these 
means  he  lays  a  broad  basis  of  personal  experience.  By 
these  means  he  is  made  fit  for  social  intercourse.  For  so 
he  learns  the  signs  in  which  racial  experience  is  expressed : 
gestures  and  attitudes,  manners  and  customs,  and,  most  of 
all,  words.  The  circumstances  of  his  nurture  compel 
imitiation.  Only  the  same  signs  that  others  use  will  be 
understood.  And  by  continual  imitation  he  establishes 
automatic  habits  like  those  of  other  members  of  society. 
His  social  conduct  takes  on  forms  that  are  like  to  the  in- 
stincts of  animals  in  their  fixity,  and  he  becomes  a  fit  and 
acceptable  member  of  society.  The  moral  person  is  he 
whose  acts  are  in  accord  with  the  accepted  rules  of  conduct 
for  the  community. 

But  society  is  an  organism,  and  therefore  adaptable. 
Just  as  there  are  common  emotions,  ruling  as  with  an  iron 
hand  the  general  conduct  of  the  people,  so  also  there  is  a 
common  intelligence  that  may  find  better  modes  of  action. 
It  may  seem  at  times  to  exert  but  little  influence. 
Appeals  to  instinctive  habits  always  bring  tumultuous  re- 
sponses; for  racial  nerve  paths  are  thoroughly  well  broken 
for  stimuli  to  eat,  to  drink,  to  fight  and  to  indulgence  of  the 
baser  passions;  and  the  plea  for  better  things,  may  often 
seem  to  fall  on    deaf   ears.     The  prophets  and  seers   who 


RESPONSIVE  LIFE  OF  ORGAXISMS  511 

have  sought  to  extend  pubhc  vision  may  at  times  seem  to 
have  labored  in  vain.  But  in  the  social  as  in  the  physical 
organism,  in  the  long  run,  intelligence  wins. 

Trial  and  error  was  at  first  the  sole  method  of  progress; 
but  society  learned  to  imitate  and  has  improved  by  imita- 
tion; and  it  has  learned  to  initate  new  activities  and  to  inhijj- 
it  old  ones  by  reason  of  clearer  discernment  of  the  truth. 
We  no  longer  piously  burn  witches,  or  beat  lunatics  to 
dreve  the  devils  out  of  them. 

Society,  therefore,  having  taken  stock  of  its  experiences, 
has  instituted  some  integrating  forces  of  its  own.  Educa- 
tion is  the  chief  of  these:  universal  education;  for  organic 
health  is  impossible  unless  all  the  parts  of  the  organism  be 
properly  responsive  to  common  needs.  Instruction  now 
brings  within  reach  of  the  individual  the  best  things  of  racial 
experience,  both  past  and  present;  and  if  there  be  discern- 
ment, practice  develops  in  him  the  appropriate  modes  of 
action. 


APPENDIX. 

I.     Preliminary  outline  on  lenses,  lighting,  focusing,  cover- 
ing, finding,   etc. 

1.  The  crystalline  lens  of  the  eye  is  adjusted  by  change 
of  shape,  effected  by  voluntary  muscles.  Hold  a  pencil 
between  the  eye  and  a  distant  window  and  try  to  see  pencil 
and  window  sash  at  the  same  time.  Note  the  distinct  mus- 
cular effort  within  the  eye  at  each  shift  of  vision  from  one 
object  to  the  other.  Repeat  with  the  window  sash  and  a 
tree  on  the  horizon. 

2.  Artificial  lenses,  being  of  permanent  shape,  are  ad- 
justed or  focused  by  change  of  position,  altering  the  dis- 
tance from  the  object.  Move  a  large  simple  lens  forward 
and  backward  between  the  eye  and  the  letters  of  a  printed 
page  until  a  clear  and  enlarged  image  of  the  letters  is  ob- 
tained. Note  that  there  is  but  one  place  of  clear  vision  :  at 
this  place  the  lens  is  in  focus.  Observe  whether  two  lenses 
of  different  size  focus  at  the  sa,me  distance  from  the  page. 

3.  Catch  the  nearly  parallel  rays  of  light  from  a  distant 
window  in  the  larger  lens,  and  focus  them  on  a  sheet  of  white 
paper  held  behind  the  lens.  When  focused,  a  clear  minia- 
ture picture  of  the  window  will  appear  upon  the  paper. 
Measure  the  distance  from  the  optic  centre  of  the  lens  to  the 
paper;  this  is  the  focal  distance  of  the  lens.  Try  the  other 
lens  and  determine  its  focal  distance.  The  curvature  of  the 
surface  of  a  lens  mainly  determines  its  focal  distance,  and 
also  its  magnifying  power.  The  magnifying  power  of  any 
simple  lens  is  easily  computed  by  the  following  formula: 


10 


M,  wherein  10  is  ten  inches,  the  focal  distance  of  the 

normal,  unaided  eye,  when  viewing  small  objects,  /  equals 
the  focal  distance  of  the  lens  in  question  (measured  as  above) , 


514  GENERAL  BIOLOGY 

and  M  equals  the  magnification.  Substituting  the  values 
you  have  found  /  to  have  for  your  two  lenses,  determine 
their  magnification. 

4.  The  objective  of  the  compound  microscope  is  practi- 
cally a  simple  lens.  Take  the  shorter  of  the  two  objectives 
in  hand  and  examine  with  it  the  stippled  background  of  a 
printed  halftone  figure  (such  as  figure  2,  on  page  8  in  this 
book).  Then  try  the  longer  objective,  and  observe  the 
shortening  of  focal  distance  with  increasing  magnification. 
Obviously,  we  soon  reach  the  limits  of  practicability  of 
simple  lenses. 

5.  Hence,  the  compound  microscope,  with  its  eyepiece 
for  magnifying  the  already  enlarged  image  produced  by  the 
objective.  Examine  again  the  half-tone  stippling  with  the 
low  power  objective  used  as  a  simple  lens  and  note  the 
apparent  size  of  the  stipple  marks;  (Better  use  for  this  and 
the  following  a  detached  slip  of  paper  printed  in  halftone, 
for  convenience  in  placing  under  microscope)  then  attach 
this  objective  to  the  microscope,  insert  the  longer  (if  there 
be  two)  of  the  eyepieces  in  the  top  of  the  microscope  tube; 
place  the  stippling  on  the  stage  directly  under  the  objective, 
focus  and  again  note  the  apparent  size  of  the  stippling.  The 
magnification  of  the  compound  microscope  is  determined  by 
multiplying  that  of  the  objective  by  that  of  the  eyepiece. 
Suppose  that  your  objectives  are  of  two-thirds  inch  and  one- 
fifth  inch  equivalent  focus,  and  your  eyepieces,  of  one  inch 
and  one-and-one-half  inch,  respectively:  what  will  be  the 
magnifying  powers  of  the  four  possible  combinations? 

6.  Observe  the  effect  of  pushing  in  and  pulling  out  the 
draw  tube  of  the  microscope  on  the  apparent  size  of  the 
object.  The  lenses  of  the  usual  laboratory  microscope  are 
corrected  for  (and  so,  will  give  the  best  results  with)  a  tube 
length  of  160  millimetres. 


APPENDIX 


515 


Uncontrolled  refraction  of  light  rays,  producing  distortion  of 

image. 

1.  Dip  the  front  of  a  simple  lens  in  water,  and,  without 
wiping  it,  look  through  it  in  the  letters  of  a  printed  page. 
You  have  altered  the  curvature  of  the  surface  first  met  by 
the  rays  of  light  coming  from  the  print,  deflecting  them  out 
of  their  proper  course. 

2.  With  the  low  power  objective  in  place  on  the  micro- 
scope and  clean,  the  eyepiece  in  place,  and  some  object 
clearly  in  focus,  touch  the  front  of  the  objective  lightly  with 
the  moist  finger,  and  observe  how  the  appearance  of  the 
object  is  altered.  The  fingers  are  never  optically  clean. 
The  slightest  deposit  on  the  surface  of  a  lens  disturbs  its 
refracting  harmony.  Do  not  touch  the  glass  of  your  lenses 
with  the  finger  again,  nor  with  anything  else,  except  on  the 
occasions  (which  will  then  be  rare)  when  it  is  necessary  to 
clean  them. 

3.  To  clean  a  lens,  moisten  it  with  the  breath  and  wipe 
dry  with  soft  lens  paper  (or  with  a  very  soft  old  linen  hand- 
kerchief) ;  when  more  than  this  is  needed,  take  it  to  the 
instructor. 

4.  Place  a  little  tuft  of  green  algae  upon  a  slide,  wet,  and 
examine  it  with  a  lens.  Then  lower  a  cover  glass  upon  it, 
fill  up  beneath  the  cover  with  water  and  examine  again. 
The  cover  gives  the  flat  upper  surface  that  is  necessary  to 
prevent  uncontrolled  refraction  and  distortion  of  image. 
Complete  immersion  in  a  watchglass  of  water  would  give  a 
similar  result.  You  cannot  well  examine  an  object  half 
wet  and  half  dry.  Dry  objects  may  be  examined  with  low 
power  lenses  uncovered,  but  you  must  always  use  a  cover 
glass  with  the  high  power  objective. 

5.  Air  entangled  under  the  cover  glass  is  a  frequent 
source  of  trouble.  The  air  may  cling  to  the  cover — will  be 
likely  to  do  so  if  the  cover  be  dropped  flat  upon  the  object. 


5i6  GENERAL  BIOLOGY 

Breathe  upon  one  side  of  the  cover  to  moisten  it,  and  let  it 
down  with  one  edge  in  advance  of  the  other. 

6.  The  air  may  cUng  to  the  object.  For  example, 
mount  a  dry  thread  in  a  drop  of  water,  cover  and  examine 
with  low  power.  Alcohol  may  be  used  to  remove  the  air. 
Remount  the  thread  in  alcohol;  cover,  allow  a  little  time  to 
soak,  and  observe  the  disappearance  of  the  air.  Air  bub- 
bles are  generally  present  in  freshly  mounted  slides,  and 
must  be  recognized,  and  not  confused  with  structures. 
Note  the  peculiarities  of  their  refraction  at  different  foci,  and 
learn  to  recognize  an  air  bubble  instantly. 

On  locating  dirt  that  is  in  the  field  of  vision. 

1.  It  may  be  on  eyepiece,  objective,  slide,  condenser  or 
mirror.  To  tell  whether  it  is  on  the  eyepiece,  rotate  the  eye- 
piece while  looking  through  it;  if  there,  the  dirt  will  rotate 
with  the  eyepiece. 

2.  To  tell  whether  it  be  on  the  objective,  change  focus; 
if  there,  it  will  give  the  same  obscurity  at  all  foci. 

3.  If  it  be  on  the  slide,  it  may  be  located  by  moving  the 
slide  or  cover;  it  will  move  with  the  slide,  and  may  readily 
be  focused  upon;  the  two  sides  each  of  slide  and  cover 
offer  four  levels  at  which  it  may  be  found.  There  is  no 
excuse  for  using  dirty  slides  or  covers,  or  for  allowing  dirt 
upon  condenser  or  mirror,  where  it  may  be  directly  observed 
and  whence  it  is  easily  removed. 

On  the  use  of  mirror  and  diaphragm. 
I.  Learn  the  use  of  the  mirror:  i)  by  trying  both  sides 
of  it;  2)  by  trying  it  in  different  positions  of  the  swinging 
mirror  bar;  and  3)  by  taking  light  from  various  sources,  as 
the  wall,  the  ceiling,  the  curtain,  the  sky.  Then  keep  the 
mirror  bar  vertical,  and  use  the  flat  side  with,  the  concave 
side  without,  a  condenser. 


APPENDIX 


5n 


2.  Using  a  slide  of  algal  filaments,  mounted  and  covered 
as  before,  examine  some  favorably  exposed  green  filaments, 
using  all  the  sizes  of  diaphragm  you  have  available  in  suc- 
cession, and  finally  using  no  diaphragm  at  all,  oVjserving  the 
while  the  relative  distinctness  of  the  green  chlorophyl,  and 
of  the  clear  transparent  cell  wall.  Thus  you  should  learn 
the  advantage  of  stopping  out  the  excess  of  light. 

On  the  use  of  the  higher  power  lenses. 

1.  In  rapid  focusing,  while  finding  an  object  under  the 
compound  microscope,  never  run  the  objectives  downward 
while  looking  through  the  tube :  for  thus  you  would  sooner 
or  later  jam  an  objective  into  the  cover  glass,  possibly 
breaking  both.  The  objectives  as  well  as  being  the  most 
expensive  part  of  the  instrument,  are  the  parts  most  easily 
abused.  While  looking  from  the  side,  push  the  objective 
down  close  to  the  object  (close  enough  to  be  within  the  focal 
distance  of  the  objective,  previously  determined) ;  then 
place  your  eye  to  the  eyepiece  and  draw  up  slowly  till  the 
object  is  somewhat  visible;  then  finish  focusing  with  the 
fine  adjustment. 

2.  Determine  the  actual  size  of  the  field  with  the  diflfer- 
ent  combinations  of  lenses  available,  by  examining  a 
mounted  strip  of  paper  printed  with  fine  and  regular  half- 
tone stippling  (better  mounted  in  glycerine  and  covered) 
with  them  successively,  and  observing  the  extent  of  the 
stippling  included  in  the  field  with  each.  Thus  you  may 
determine  what  combination  will  be  available  for  the  exam- 
ination of  objects  of  different  size. 

3.  Learn  once  for  all  how  to  find  an  object  speedily  and 
certainly  under  the  high  power  objective;  proceed  as  fol- 
lows :  find  the  object  or  the  part  of  it  desired,  first  with  the 
low  power  objective;  then  place  the  part  of  it  to  be  exam- 
ined with  the  hi<j^h  power  in  the  centre  of  the  field,  char.ge 


5i8  GENERAL    BIOLOGY 

objectives  by  turning  the  nose  piece,  and  focus,  observing 
whether  the  lens  must  go  up  or  down,  and  how  many  turns 
of  the  fine  adjustment  screw.  If  the  two  objectives  are 
exactly  concentered,  nothing  further  will  be  necessary.  If 
not,  an  object  placed  in  the  centre  of  the  field  with  the  low 
power  may  not  be  in  the  field  at  all  with  the  high.  To  find 
where  it  is  reverse  the  process.  Pick  out  some  easily  recog- 
nizable part  seen  under  high  power;  change  objectives 
again,  and  see  where  it  lies  in  the  low  power  field.  Here 
will  be  the  place  to  put  an  object,  in  order  to  find  it  again 
imder  high  power.  Always  begin  hunting  it  with  the  low 
povv^er.  If  your  objectives  do  not  happen  to  be  concen- 
tered, the  above  process  may  have  to  be  repeated  every 
time  an  objective  is  loosened  and  its  position  changed. 
Practice  finding  things  with  high  power  until  you  can  do  it 
quickly  and  certainly. 

Practical   points   in   the  use  of  miscroscope  and   of   stage 

mounts. 

T.  Save  your  eyes,  by  proper  use  of  them.  First  focus; 
then  look. 

2.  Look  through  the  centre  of  a  lens,  not  through  its 
edges. 

3.  Look  with  both  eyes  open,  concentrating  attention  on 
what  is  before  the  one,  disregarding  what  is  before  the 
other;  this  will  save  much  weariness  of  many  facial  muscles, 
when  once  an  acquired  habit. 

4.  Never  rack  the  microscope  tube  downward  while 
looking  through  it. 

5.  Always  use  a  coverglass  with  a  high  power  objective. 

6.  Wet  objects  should  be  completely  immersed  for 
examination. 

7.  A  cover  glass  has  several  mechanical  uses:  a) 
Mounted  objects  of  some  kinds  (such,  for  example,  as  fully 


APPENDIX 


5^ 


-^ 


mature  spermaries  of  Chara)  may  Vje  crushed  beneath  it  and 
their  parts  scattered,  and  dissociated  for  study,  b)  Many 
objects  not  too  flat  may  be  turned  over,  or  rolled  into 
new  positions  for  observation,  by  pushinj^  on  the  edge  of 
the  cover. 

8.  Drop  Cultures  for  germinating  spores,  etc.,  are  made 
upon  cover  glasses.  A  drop  of  culture  fluid  is  placed  on  the 
middle  of  a  cover  which  is  then  inverted  and  laid  over  the 
open  well  in  a  hollow  ground  slide,  or  over  a  ring  of  thick 
wet  blotting  paper,  where  it  hangs  suspended  in  the  center. 
The  slide  is  then  kept  under  proper  conditions  in  a  moist 
chamber  of  some  sort,  and  is  replaced  on  the  stage  of  the 
microscope  for  examination  at  any  time  without  distur- 
bance of  the  culture. 

On  the  dissecting  of  any  of  the  larger  animals  . 

1.  Learn  to  handle  your  tools,  forceps,  scissors,  scal])el 
and  needles,  and  to  depend  on  them  for  results;  hacking  to 
pieces  is  not  dissecting. 

2.  Open  the  body  cavity  where  access  is  easiest  and 
damage  to  internal  significant  parts  is  least  likely  to  occur. 
This  will  be  the  dorsal  side  in  worms  and  arthropods,  and  the 
ventral,  in  vertebrates. 

3.  If  delicate  parts  are  to  be  seen,  immerse  under  water, 
which  will  float  them  into  better  view. 

4.  Be  careful  not  to  cut  into  any  organ  whose  contents 
will  roil  the  water  and  hinder  observation. 

5.  Fully  expose  the  organs  to  be  observed  by  pinning 
the  flaps  of  the  body  wall  out  of  the  way  as  by  i)inning  them 
to  the  bottom  of  the  dissecting  tray. 

6.  Know  what  you  arc  looking  for,  but  do  not  be  ',00 
easily  convinced  that  you  have  seen  it. 


520  GENERAL  BIOLOGY 

Concerning  laboratory  drawings. 
Draw  the  thing  as  you  see  it,  but  first  be  sure: 

1.  That  you  see  the  right  thing;  don't  draw  dirt  or  air 
bubbles. 

2.  That  you  see  it  in  normal  condition;  look  your 
material  over,  and  make  sure  what  is  normal;  and  then 
don't  draw  distortions  or  freaks. 

3.  That  you  see  the  significant  things;  and  then  don't 
draw  endless  repetitions,  such  as  whole  sections  of  similar 
cells — but  represent  those  things  that  mean  something  to 
you. 

4.  Don't  draw  what  you  can't  see. 

5.  Draw  with  as  few  lines  as  possible  (smearing  with  a 
pencil  is  not  drawing) ;   shading  is  usually  unnecessary. 

6.  In  starting  a  drawing,  look  to  proportions;  usually 
there  are  a  few  main  structural  lines  discoverable,  and  if 
these  are  first  laid  down  with  a  little  care,  a  well  propor- 
tioned drawing  is  easily  built  upon  them. 

7.  Use  mechanical  means,  especially  for  diagrams,  when 
the  subject  admits  of  it;  forms,  or  a  compass  for  m_aking 
circles,  and  a  ruler  for  parallel  lines,  etc. 

2.     Materials  for  practical  studies. 

A  few  suggestions  are  here  made  as  to  useful  ways  of 
handling  the  materials  that  are  less  familiar  to  the  experience 
of  the  average  laboratory  student  at  the  present  time. 

On  collecting  and  concentrating  aquatic  organisms.  A 
very  simple  and  inexpensive  outfit  will  procure  these  organ- 
isms in  very  great  variety  and  abundance,  and  with  little 
expenditure  of  time. 

I.  A  cone-shaped  dip  net,  some  four  inches  in  diameter, 
on  a  long  light  handle.  The  cone  may  be  made  of  fine  swiss, 
of  China  silk,  or,  better  of  no.  12  silk  bolting  cloth.  Swept 
through  the  water  the  plankton  is  swept  into  the  point  of  the 


APPENDIX  521 

cone,  and  is  easily  transferred  therefrom  to  a  beaker  of  clean 
water  by  everting  the  cone  on  the  tip  of  one's  finger  and 
washing  it  off  in  the  beaker. 

If  a  more  expensive  net  is  allowable,  a  plankton  towing 
net  a  yard  long  of  silk  bolting  cloth,  that  may  be  drawn  from 
the  end  of  a  long  pole,  will  gather  the  material  faster  and 
will  be  better  for  use  in  open  water,  but  not  for  use  in  the 
little  openings  along  the  shores. 

2.  A  few  small  strainers  of  different  mesh,  for  sorting 
organisms  according  to  size. 

3.  Some  sort  of  concentrating  apparatus  for  getting  the 
organisms  together  so  that  a  number  of  specimens  may  be 
obtained  with  each  drop  of  water  taken  up  with  a  pipette. 
An  excellent  one  may  be  made  as  follows :  Fold  a  piece  of 
fine-meshed  cloth  (bolting  cloth,  preferably)  filter  ]japer- 
fashion,  and  place  it  in  a  small  funnel.  Set  the  funnel  in  a 
jar  level  full  of  water  with  a  mouth  wide  enough  so  that  the 
point  of  the  cloth  in  the  funnel  will  be  immersed  half  an 
inch.  Set  the  jar  in  a  larger  vessel  to  catch  the  overflow, 
and  then  pour  the  water  containing  the  organisms  into  the 
funnel  until  the  desired  concentration  has  been  reached.  A 
rubber  hand  bulb  on  a  glass  tube  will  be  of  assistance  in 
transferring.  Some  such  apparatus  will  be  useful  for 
gathering  the  material  needed  for  studies  10,  11,  15,  16,  20, 
46  and  49. 

Collecting  of  the  larger  organisms  will  require  a  dip  net  of 
the  ordinary  shallow  sort,  so  shaped  that  things  can  be 
examined  outspread  upon  it  as  lifted  from  the  water.  Dip 
nets  will  be  most  useful  for  gathering  the  material  needed  in 
studies  37,  41,  43,  48,  49,  53  to  58,  and  62.  Here,  also,  a 
collecting  seine  will  be  more  efficient  for  collecting  larger 
organisms  in  open  water. 

A  cyanide  bottle  for  collecting  insects  is  easily  made  from 
any    wide   mouthed    bottle  by   placing    some   cyanide  of 


522  GENERAL    BIOLOGY 

potassium  (one  fourth  ounce  more  or  less  for  a  pint  bottle) 
in  the  bottom,  covering  it  with  dry  sawdust  (or  other  good 
absorbent)  and  fastening  it  in  the  bottom  with  several 
discs  of  thick  blotting  paper.  Gum  the  edges  of  the  blot- 
ting paper  discs  before  pressing  them  into  place.  After 
the  gum  dries,  cork  tightly,  afhx  a  POISON  label,  and  keep 
it  out  of  the  way  of  small  children.  An  insect  net  is  a 
valuable  adjunct  to  the  cyanide  bottle,  but  the  collecting 
required  for  studies  2,3,4,  5,  and  59  may  all  be  done  with 
the  bottle  alone  if  it  be  dexterously  used. 

Swarms  and  occasions  of  special  abundance  should  be 
taken  advantage  of  by  one  who  has  to  keep  a  laboratory 
supplied.  It  is  often  possible  to  get  enough  of  certain  kinds 
of  material  to  last  for  years  at  a  few  strokes  of  a  net,  but  the 
opportunity  may  be  a  brief  one,  and  not  regularly  recurring, 
as  in  the  autumnal  swarming  of  the  milkweed  butterfly. 
Such  studies  as  no.  41  may  seem  to  demand  a  lot  of  prelimi- 
nary collecting  of  material;  but  with  the  wide  range  of 
material  allowed,  and  the  remarkable  abundance  of  all  of 
the  types,  it  may,  with  foresight,  be  had  with  remarkably 
little  time  and  labor  spent  in  getting  it  together.  For 
example,  one  can  go  to  the  ledges  of  stone  in  the  bed  of 
almost  any  rapid  creek  in  early  autumn  and  sweep  up  in  a 
few  minutes  enough  black-.^y  larvae  to  last  a  laboratory  a 
life  time. 

Permanent  cultures  of  the  insects  needed  for  study  41, 
and  for  some  of  those  of  study  48,  may  be  easily  main- 
tained in  the  laboratory.  Meal  worms  or  bean  weevils  may 
be  raised  in  a  closed  bin  of  shorts  or  of  beans,  respectively, 
needing  only  the  occasional  removal  of  the  excess  of  ani- 
mals and  the  renewal  of  their  provender.  Mosquitoes  and 
midges  and  certain  mayflies  from  pools  may  be  raised  in 
covered  vessels  of  rain  water. 


APPENDIX  523 

Eggs  of  pond  snails  (Physa,  etc.)  for  study  37  may 
usually  be  obtained  in  late  winter  by  bringing  the  snails  in 
from  the  ponds,  where  they  may  easily  be  picked  from  bot- 
tom trash  or  from  floating  boards,  and  placing  them  in  bowls 
of  clean  water.  Provide  them  with  bits  of  cress  or  cabbage 
or  other  fresh  leaves  to  eat.  Within  twenty-four  hours  the 
elongated  and  transparent  egg  masses  will  Ijegin  to  appear, 
sticking  to  the  sides  of  the  vessel.  The  vessel  should  be 
kept  clean,  for  silt  adhering  to  the  gelatinous  covering  will 
hinder  observation.  The  egg  masses  may  be  divided  into 
small  parts  and  distributed  for  study. 

Planarians  for  study  42  may  be  picked  from  stones  lifted 
out  of  a  clean  creek  bed  or  out  of  the  surf  on  the  shore  of  a 
lake,  or  often  from  the  trash  in  a  spring  pool. 

Carriers  for  handling  the  numerous  plants  in  thumb  pots 
needed  in  study  38  may  be  made  by  partly  filling  any  shal- 
low tray  with  wet  sand,  and  soldering  stretched  poultry 
netting  of  suitable  mesh  across  the  top.  Set  the  pots  in  the 
sand.  The  wires  will  prevent  their  toppling  over,  and  they 
may  easily  be  carried  back  and  forth  as  may  be  necessary 
between  laboratory  and  greenhouse  (or  lighted  window). 

Grafting  wax  (for  study  44) : 
Rendered  tallow  i  part. 
Beeswax  2  parts. 
Resin  4  parts. 

Melt  together  with  heat;  pour  into  a  pail  of  cold  water; 
pull  (like  taffy)  until  light  colored;  and  put  away  for  use. 
The  heat  of  the  hands  will  soften  it  sufficiently  for  applica- 
tion. 

Grafting  is  to  be  attempted  in  spring  just  before  growth 
starts.  Cions  are  better  kept  over  winter  in  a  cool  cellar 
in  moist  (not  wet)  sand,  but  can  be  cut,  if  still  dormant  for 
immediate  use.  Seedlings  to  be  grafted  can  readily  be 
grown  in  a  garden,  but  large  trees  are  often  available,  and 
wild  crab  apples,   in  the  woods.     The  operation   of  bud 


524 


GENERAL    BIOLOGY 


grafting    (budding)    is   available   for  late   summer,   where 
mature  buds  are  selected  for  immediate  transplantation. 
Cone  galls  needed  for  study  42,  abound  on  the  tips  of  the 

twigs  of  our  common 
glaucous  willows, 
along  streams  and  in 
sunny  wet  places 
generally.  The  gall 
midge  larvae  spend 
the  winter  in  the  galls, 
fully  grown,  and 
transform  in  early 
spring.  If  brought 
into  the  laboratory 
any  time  after  Christ- 
mas (or  after  heavy 
freezing  has  occurred) 
they  will  enter  the 
pupa  stage  in  a  few 
weeks  or  less  and 
adults  will  appear  two 
weeks  thereafter.  In- 
dividual lots  collected 
by  students  may  by 
them  be  tied  up  in 
squares  of  cheese- 
cloth, and  the  midges 
will  develop  normally 


Fig.  285.  Diagrams  of  the  leg  structures  of  diving  beetles.  ^,  the  hind  leg  of 
Laccophilus.  r,  trochanter.  5,  femur,  t,  tibia,  x,  the  overlapping  lobe  or  brace 
of  the  femur  that  limits  and  guides  the  action  of  the  tibia  1,  2,  3,  4,  5,  the  seg- 
ments of  the  tarsus,  e,  the  single  claw  c,  c,  c,  c,  c,  c,  c,  jumping  spines,  v,  v, 
swimming  fringes,    z,  tibial  spurs. 

b,  two  segments  from  the  middle  of  the  tarsus,  showing  at  n  the  little  transverse 
group  of  apical  bristles  characteristic  of  Acilius  and  its  allies. 

c,  the  knee  joint,  showing  at  m  the  linear  group  of  setae  that  is  characteristic  of 
Agabus  and  its  allies.  /,  femur,     t,  tibia. 


APPENDIX 


525 


if  the  galls  be  wetted  about  once  a  week,  (as  by  holding 
them  under  the  water  tap,  or  by  immersing  them  for  a 
minute  in  a  bowl  of  clean  water).  Data  given  in  chapter 
I,  (pages  44  and  45),  will  suffice  for  distinguishing  the 
midge  larvae  from  their  parasites  (which  are  sure  to  be 
numerous)  and  from  the  other  occupants  of  the  galls.  (See 
figure  36  on  page  46.) 

A  biological  garden,  while  not  absolutely  required,  is  the 
best  possible  equipment  for  the  sort  of  a  course  this  book 
proposes.  It  need  be  a  little  more  than  a  pond  or  a  brook, 
and  a  few  little  border  plantings.  There  should  be  enough 
of  it  for  supplying  stores  of  fresh  materials  for  class  use, 
and  enough  for  connecting  the  work  of  the  student  upon 
living  things  with  the  world  of  which  they  are  a  part. 

If  time  can  be  taken  for  but  one  of  the  introductory 
studies  on  the  relations  between  flowers  and  insects,  Study 
5  is  the  one  that  should  be  chosen.  Full  blooming  clumps 
of  flowers  (preferably  of  some  specialized  bumble-bee 
flower,  such  as  the  snap-dragon,  the  great  blue  lobelia, 
butter  and  eggs,  or  turtle-heads)  will  be  needed.  If  not 
accessible  in  nature,  they  may  be  easily  provided  with  a 
little  forethought  at  planting  time:  all  give  handsome 
landscape  effects  in  border  plantings. 

For  the  series  of  ecological  studies  on  diving  beetles 
(studies  55  to  58  inclusive),  some  means  of  determining  the 
beetles  being  needed,  a  key  to  the  North  American  genera  in 
the  family  Dytiscidae  is  presented  on  the  following  pages. 
The  number  of  our  species  in  each  genus  is  indicated  by 
the  arabic  numeral  standing  before  the  name  of  the  genus 
(in  parenthesis) :  and  limited  distribution  is  indicated  by 
abbreviations  for  the  name  of  the  region  in  which  it  is  known 
to  occur. 


526 


GENERAL  BIOLOGY 


Fig.  286.  A  diving  beetle  (Coptotomus 
inierrogatus) .  The  scutellum  is  the 
small  triangular  piece  lying  between 
the  bases  of  the  wing-covers,  or  elytra. 


Fig.  287.  Diagram  of  the  ventral  as- 
pect of  a  diving  beetle  {Coptotomus  in- 
ierrogatus) a,  antenna;  b,  mouth;  c,  c, 
coxal  cavities  for  the  fore  and  middle 
legs;  d,  labial  palpi;  ^,  eye;/,  maxillary 
palpi;  g,  lateral  margin  of  the  protho- 
rax ;  h,  epipleura  of  the  wing  cover  (ely- 
tron);  i,  prosternal  orocess;  j,  metaster- 
nal  fork;  k,  hind  coxa  with  /,  the  inner 
and  0,  the  outer  laminae;  p,  the  coxal 
process  and  q,  the  coxal  notch;  r,  tro- 
chanter of  the  hind  leg;  s,  femur;  t, 
tibia;  u,  hind  tarsus  of  five  joints;  v, 
spu  s  of  the  middle  tibia.  /,  2,  j,  4,  3,  6, 
ventral  abdominal  segments,  sf^ ,  st^,  sP, 
sterna  of  pro-,  meso-,  and  meta-thorax,  respectively;  w,  wing  of  the  metaster- 
num.  m,  episternum,  and  n,  epimercn  of  the  successive  thoracic  segments.  The 
coxal  line  is  the  line  extending  between  /  and  o  in  the  figure,  and  the  coxal  bor- 
der is  the  part  of  the  coxal  process,  p,  that_is  marked  ofE  laterally  by  the  posterior 
end  of  the  coxal  line. 


.     KEY  TO    THE   GENERA    OE     ADULT    DYTJS- 
CIDAE— DIVING  BEETLES. 

1.  Third  joint  of  the  fore  and  middle  tarsi  deeply  bi- 

lobed,  the  fourth  joint  rudimentary  or  wantin^^.      2 
Third  and  fourth  joints  not  greatly  different  from 
the  others 8 

2.  Scutellum  visible  (S.  U.  S.)  •  •  (2) Celina 

Scutellum  invisible 3 

3.  Hind  coxal  processes  each  divided  by  a  deep  pos- 

terior notch,  the  inner  ramus  oppressed  against 
the  first    abdominal  segment  (6) .  .  .  .  HydrovaUis 
Hind  coxal  processes  not  so  formed 4 

4.  Hind  margin  of  outer  lamina  of  hind  coxa  grown 

solidly  coherent  by  its  margin  with  the  first  ven- 
tral segment  of  the  abdomen 5 

Hind  margin  of  hind  coxa  overlapping  but  not 
coherent  with  the  first  ventral  segment  of 
abdomen 6 

5 .  Prosternal  process  broad  and  short  with  obtuse  hind 

margin;     middle    coxae    conspicuously    separate 
(16) Bidcssiis 

Hind  end  of  prosternal  process  rhomboidal;  middle 

coxae  more  approximate  (4) Desmopachna 

b.  A  thin  flat  angulate  process  springing  from  the  longi- 
tudinal ridge  that  extends  along  the  under  side  of 
the  wing  covers  near  their  side  margins  (visible 
only  if  the  wing  covers  are  lifted  and  viewed  from 
beneath)  (18) Coelamhns 

No  such  free  process  beneath  the  wing  covers 7 

7.  The  mesosternal  fork  connected  with  the  intercoxal 
process  of  the  metastemum  (72) .  .  .  .Hydroporus. 

The  mesosternal  fork  not  connected  with  the  inter- 
coxal process  of  the  metasternum(4) .  .Dcronecics. 


528  GENERAL  BIOLOGY 

8.  Scutellum  invisible 9 

Scutellum  visible 13 

9.  Prosternal  process  broadly  dilated  and  truncated 

behind;    joints  of  the  hind  tarsi  simple,  without 

broadly  over-lapping  lobes 10 

Prosternal  process  compressed  and  pointed  behind; 
joints  of  the  hind  tarsi  with  broad  over-lapping 
external  lobes  (fig.  285.4)     (13) Laccophilus 

10.  A  more  or  less  conspicuous  curved  spur  or  hook  on 

the  apex  of  the  front  tibiae 11 

No  such  hook  present  on  front  tibiae  (S.  U.  S.)      (i) 

Notomicrus 

11.  Prosternum  strongly  angulate  in  the  middle;   body 

nearly  globose;   last  joint  of  palpi  emarginate  at 
tip ;  hind  coxal  cavities  separate ;  length  3.5  mm. 

(S.  U.  S.)      (i)    Colpius 

Prosternum  flat;   hind  coxal  cavities  contiguous.  .    12 

12.  Prosternal  process  very  broad  behind;    hind  tibiae 

very  broad;     length   4  to  7  mm.(E.  U.  S.)        (i) 

H  ydrocanthus 

Prosternal  process  moderately  broad  behind;   hind 

tibiae  rather  slender;    length  less  than  4  mm.  (5) 

Canthydrus 

13 .  Inferior  spur  of  hind  tibiae  dilated,  much  broader  than 

the  other  spur  (5) Cyhister 

The  two  spurs  of  hind  tibiae  of  equal  or  nearly  equal 
breadth 14 

14.  Distal  margin  of  the  segments  of  the  hind  tarsi  beset 

on  the  outer  side  with  a  transverse  row  of  minute 

appressed  bristles  (Fig.  285/)) 27 

No  such  row  of  appressed  bristles  across  the  ends  of 

the  tarsal    segments 15 

1 5 .    Front  margin  of  the  eye  circular ;  the  last  two  pairs 
of  abdominal   stigmata   greatly   enlarged,   each 


APPENDIX  529 

'  attaining  a  diameter  equal  to  one  fourth  the  width 
of  the  abdomen     (11) Dytiscus 

Front  margin  of  the  eye  more  or  less  deeply  notched, 
by  the  intruding  margin  of  the  front  of  the  head; 
stigmata  nearly  uniform  in  diameter 16 

16.  A  linear  group  of  minute  setae  present  upon  the  pos- 

tero-external  angle  of  the  hind  femur  (fig.  285c) .  .  17 

No  such  linear  group  of  setae  present 21 

17.  Claws  of  the  hind  tarsus  equal,  and  joints  sim])le.  .  18 
Hind  tarsus  with  its  claws  unequal,  and  its  joints 

produced  posteriorly  in  overlapping  lobes     (16) 

Ilybius 

18.  Palpi  with  the  terminal  joint  dilated,  that  of   the 

labial  palpi  sub-quadrate  (Calif.)    (i)  Hydrotnipes 
Palpi  with  the  terminal  joint  not  conspicuously  di- 
lated        19 

19.  Wing  of  the  metasternum  wedge-shaped 20 

Wing  of  the  metasternum  linear,  and  dcflexed  around 

the  front  border  of  the  external  lamina  of  the  hind 
coxa  (8) Ilyhiosoma 

20.  Coxal  lines  very  deep  and  nearly  straight  (Calif.)  (i) 

.4  gab  inns 
Coxal  lines  fine  and  sinuous  (48) Agabus 

21.  Last  joint  of  palpi  emarginatc  at  tip  (3)  Coptotomus 
Last  joint  of  palpi  rounded  or  truncate  at  tip 22 

22.  Prosternum    with    a    deep   median      longitudinal 

groove    (i)    E.  U.  S Mains 

Prosternum  not  grooved 23 

23.  Claws  of  the  hind  tarsi  equal,  movable 24 

Claws  of  the  hind  tarsi  unequal,  the  outer  one  fixed   25 

24.  The  coxal  border  very  broad  (i) \gabctcs 

The  coxal  border  very  narrow    (2)  Copelatiis 

25.  Upper  surface  of  the  body  conspicuously  reticulate 

(2)    Scutoptcrns 


530  GENERAL  BIOLOGY 

Upper  surface,  if  sculptured,  not  reticulate 26 

26.  Metasternal  groove  broad  and  definite;    length  not 

over  1 5  mm.  (10) Rhantus 

Metasternal    groove    narrow    and    indistinct     (8) 

Colymibetes 

27.  Prothorax  with  a  narrow  lateral  raised  margin      (i) 

Eretes 
Prothorax  without  such  a  margin 2C 

28.  Spurs   of  hind  'tibiae    acutely   pointed   at     tip    (4) 

Hydattcus 
Spurs  of  hind  tibiae  emarginate  at  tip 29 

29.  Elytra  closely  punctate  (3) Acilius 

Elytra  not   punctate 30 

30.  Middle    femora    beset    with    elongate    setae      (7) 

Thennonectes 
Middle  femora  beset  with  short  and  stout  setae     (3) 

Graphoderes 


^■Wsi!Br0 


/' 


«»  —  ' 


.»     \ 


Hydropcrus    uadulatus. 


INDEX 


PAGE 

Abdomen   17 

Aberrancies  of  regeneration  358 

Acarina    43 

Accessory  chromosome.  .  .  301 

Acorns    5 

Active  or  motor  organs  ...  436 

Adaptation    287,459 

Adaptation   in   the  indivi- 
dual    457 

Adaptations  of  flowers   ...  11 

Adaptations  of  insects.  ..  .  17 

Adaptive  radiation 239 

Adjustment 14,  368 

Adjustment  in  form  and 

appearance    404 

Aeschna 427 

Aestivation    376 

Age  of  Stone 494 

Agassiz 224 

Air-swallowing    182 

Ajax  butterfly 308 

Alaus    429 

Albinism    316 

Alcohol 94 

Algae 56,  105,  119,334 

Alimentary  canal    .164,186,197 

Alternation  of  hosts 340 

Allantoic  artery 215 

Allantoic  vein 215 

Allantois    215 

Alternation  of  generations 

124,330 

Alternative  inheritance ...      310 

Altricial  birds 323 

Amblyopsidas    288 

Ambystoma 179,  257 

Amoeba    68,  437 

Ammophila 490 

Amnion    215 

Amphibian 214 

Anabolism   90 

Analogy 224 

Anaphase 294 

Anax  Junius 413 

Angiosperms 152 


PAGE 

Animal  coloration 422 

Animal  galls 38 

Animal  series 156 

Animism    502 

Annual  rings 147 

Annulus 135 

Antennae 17 

Antennal  hairs 447 

Antennaria    359 

Anterior  abdominal  vein .  .  188 

Anther 9 

Antheridium 122 

Antler 365 

Antipodal  nuclei   153 

Antiseptics 98 

Ants 10,  48 

Ant  sheds 50 

Aortic  arches 165 

Apes 485 

Aphids 38,  47,  306 

Aphidae 43 

Aphid  eggs 52 

Aphid  gall    38 

Apocynum 366 

Appendages 181,  231 

Apposition 114 

Aquatic  insects 407 

Archaeology 493 

Archaeopteryx 248 

Archegonial  disc 123 

Archegoniophore 122 

Archegonium 122,129 

Arch-enteron 171,  197 

Arcs    465 

Aristotle 470 

Artificial  fertilization  ....  304 

Artificial  division ^53 

Artificial  selection 279 

Artisan  stage 496 

Asellus 233 

Ascomycetes 96 

Asexual  reproduction  ....  331 

Asexual  reproductive  cells  ^t,^ 

Asparagin     85 

Assimilation    329 


S3  2 


GENERAL  BIOLOGY 


PAGE 

Assimilatory  parenchyma .  120 

Association  fibers 463 

Aster 293 

Atrophy 252 

Attitude 425 

Auditory  nerve 463 

Auk 7 

Auricle   187 

Autogenetic  responses  ...  474 

Avoiding  reaction 73,  440 

Axial  skeleton   181 

Axone 450 

Back  boned  animals 180 

Bacteria 69,  97,  173 

Balance  in  nature 6,325 

Barbarian    500 

Beak 240,  242 

Bee    8,458 

Behavior  of  organisms ...  .      435 

Bilateral  svmmetry    288 

Bile  duct  ' 186 

Bimana    485 

Binder    251 

Biogenetic  law 257 

Biophores     301 

Birch 341 

Bird's  brain 201 

Birth 217 

Birth  fate 327,  501 

Bison    7 

Bittern 398 

Bladderwort    252 

Blastopore 171 

Blastula_ _ 171,  255,  358 

Blended  inheritc\nce   .  .  .310,  316 

Blood  gills 408 

Blood  vessels 201 

Blue  flag 380 

Body  cavity 164 

Body'' asm    .  .  113,  291,  296,  363 

Bone 184 

Bcnbus 431 

Bombylius  major 34 

Brain'  .  .  .  189, '196,  257,  455,  486 

Brain  paths 458 

Bread  making 94 

Breast  bone   42 

Breeding  h.  '  its 441 

Bronchial  tubes 187 


PAGE 

Brooks  quoted 368 

Blepharocera 244 

Bryophytes 118 

Bryozoans 336 

Budding 92,  331 

Buds 158 

Bud  variation    332 

Bumblebee 30,  429 

Burdock 476 

Burdock  moths   425 

Bur  marigold 271 

Butter  and  eggs 273 

Buttercup    11 

Butterfly    .21,24 

By-paths  in    the    nervous 

system    452 

By-paths  of  the  brain  ....      465 

Caddisfiy    475 

Caddis-worms 477 

Callings    505 

Calosoma 417 

Calyptra 126 

Cambarus 233 

Cambium 145,  361 

Canoe    492 

Capillitium 102 

Carbohydrates 83 

Carbon   130 

Carbon  dioxide 83 

Cardo 18 

Carmine   73 

Carpus    259 

Carriers    523 

Carrion  beetle 429 

Carrion  flower 476 

Case  building ,  .      479 

Castle  quoted 314 

Castration    319,443 

Casualties 6,  276 

Caterpillars    472 

Cat  fishes 242 

Cave  bear 495 

Cave  dwellers 500 

Cecidomyidae     44 

Celithemis    410 

Cell  differentiation 170 

Cell  division 109,  121,  293 

Cell  multiplication 170 

Cell  wall 58,  59 


INDEX 


533 


PAGE 

Centralization   497 

Centrosome 293,  295 

Cephalization    455 

Ceratium    106 

Ceratopogon    409 

Cercomonas 1 1  o 

Cerebellum 192,  200,  461 

Cerebral  hemispheres   .... 

192,  198,  200,  201,  487 

Cerebrum 459,  461 

Cervical  vertebrae 225 

Change  of  function 253 

Chara 63 ,  66,  113 

Characters  in  germ  cells .  .      311 

Charchesium 81 

Charms 505 

Chauliognathus  scutellaris         1 9 

Chelipeds 231 

Chelone    26,  252,  253 

Che  lone  glabra 29 

Chemical  elements 82 

Cheinical  engine 89 

Chemical  stimuli 444-  445 

Chickweed 143,  148 

Chicks 481 

Chironomus 409 

Chloragogue 175,178 

Chlorophyl,    58,  85,92,105,   175 

Chordata    223 

Chromosomes    .  .  .  .294,  295,  299 
Chromosome  reduction     ..      301 

Chromatin 293 

CiHa    74.  438 

Circulation 202 

Circulatory  apparatus    ...      211 

Circulatory  system   187 

Civilization    320 

CiviHzed  life 325 

Cladophora    65 

Classification 221 

Clathrocystis 65 

Cleavage 193,  303 

Climatic  and  metereologi- 

cal  conditions    284 

Clistogamous  flowers    ....        34 

Clitellum    164,  169 

Closed  galls    40 

Closterium 57 

Cockroaches 7 

Coelom    164,  184 


PAGE 

Coleochete   340 

Coleoptera   24,  42,  44 

Colias  ])r()todice  . 24 

Collaterals 450 

Collecting 520 

Colony 81,  106 

Coloration    422 

Closteriuin 112 

Columella 126 

Columns 461 

Combination  of  organisms  353 

Commensalism    400 

Commensal  nematodes  ...  178 

Commissural  fibres 462 

Common  parenchyma     ...  121 

Competition 275 

Compound  microscope  ...  514 

Concentrating  apparatus   .  521 

Conducting  tissues    132 

Cone  gall    45,  367,  524 

Conifers    149 

Conjugating  reaction    ....  441 

Conjugation 111,113 

Conocephalus    118 

Conklin  quoted 319 

Contractile  processes    ....  161 

Contractility 435 

Control  centers    508 

Control  circuits 453 

Convergence    243 

Convulsions 453 

Cooking    491 

Co-operation 495 

Coordination    453,  502 

Coptotomus 417 

Copulation 168 

Copying  pencil 411 

Coracoid  bone 259 

Cord 461 

Corethra 409,  425 

Corn 6 

Corpuscles,  white 173 

Correlation 459 

Correspondence    between 

ontogeny  and  phylogeny  255 
Cortex    .  .'147,  462,  463,  465,  487 

Correlation 265 

Costal  grooves 182 

Cottonwood 38 

Countershading 424 


534 


GENERAL  BIOLOGY 


PAGE 

Cover  glass 518 

Covering  gall 40 

Cow-bird    396 

Cradle 251 

Cranial  nerves 190,  463 

Crawfish 355 

Crickets    113,  308 

Crop 166 

Cross-breeding 315 

Cross-fertilization 129 

Cross-pollination 9 

Crossed  pyramidal  tract  .  .      466 
Cross-section  elm  bough  ..      405 

Crustacea 230,  232 

Crystalline  lens 513 

Culture  stages 499 

Curculionidae    44 

Cutting  tools 491 

Cyanide  bottle 24,  52  i 

Cynipidae 43.  44,  339 

Cynipid  galls 44 

Cynipid  larva 45 

Cynthia    312 

Cytoplasm 58 

Cytoplasmof  the  egg    ....      302 

Damselfly 376 

Darwin 266,  277 

Dasyllis    431 

Death  rate   327 

Degeneracy 327 

Degeneration 251 

Democracy    ;   ..      320 

Dendrites 450,  457,  464 

Derivation  of  tissues 175 

Derived  circuits 454 

Dessication    378 

Determinants    301 

Development 148,  170,  290 

De  Vries 274 

Differentiation    442 

Differentiation  of  habitat  .      381 

Dinobryon 106 

Diptera 20,  24,  42,  44 

Dipterous  gall  makers    ...        42 

Dissecting    519 

Dissimilation 90,  329 

Distance  receptors    455 

Distribution 127,  378 

Divergent  development  236,237 


PAGE 

Diving  beetles     415,527 

Division  of  labor 176,  508 

Domestication 51,  499 

Domestication  of  aphids    .        50 
Dominant  characters    ....      310 

Dorsal  vessel 165 

Dragonfly 410 

Draparnaldia 334 

Drawing 520 

Drepanidas 241 

Dress    506 

Drop  Cultures 104,  519 

Duckweed    332 

Dytiscidae 415,  527 

Ear 259,  447 

Earthworm    163,  359 

Ecological  differences  ....      285 

Economic  procedure 7 

Ectoderm 159,171,448 

Ectosarc 71,  105 

Education, 

318,  324,459,490,  511 

Eels 343 

Egg 122,  162,  175,  193,  291 

Elaters 124 

Elder    14 

Elementary  species 274 

Elytra 24 

Embryo 130,  151 

Embryology    .  175,  255,  258,  260 

Endoderm 159,  160,  171 

Endopodite 232 

End  organs    441 

Endryas 426 

Endosarc 105 

Endosperm    151 

Endosperm  nuclei 153,  154 

Energy 83,  90 

Enteron 164,  185,  186 

Environment 127,  291 

Epidermis, 

120,  132,  137,  143,  356 

Epistylis 82,  112 

Epitheliuin    172,  197 

Equisetum 136 

Erect  attitude   4S6 

Eremochelys  odoratus    ...      322 

Esophagus 78,  82,  166,  183 

Ethnological  classification     491 


INDEX 


53, 


PAOE 

Ethnology 493,  494 

Euglena 105,438 

Evaporation    219 

Evolution  117,  239,  264,  277,  317 

Excess  of  offspring    327 

Excess  pollen  production  10,  402 

Excess  of  young    274,  325 

Excretions 59 

Exopodite    232 

Experience 490 

Exposure   219 

Expression  of  animals    .  .  .      434 

Eyes 182,  446 

Eyespot 429,  438,445 

Eye-stalk 359 

Fallopian  tubes 215 

Fat 347 

Feathers 432 

Fecundity 325 

Felted  galls    39 

Fern 129 

Fertilization, 

9,  112,  127,  138,  150,  169,  299 

Fetishism 504 

Figwort  family    252 

Filament    9,  61 

Fire 491 

Fishes,  blind    288 

Fish    495 

Fission 109 

Fitness 26,278 

Flagellates 104 

Flagellum 105,  438 

Flag  weevil    381 

Flash  colors 427 

Flat  worm    211 

Floral  envelopes    11 

Flowers    148 

Flower  cluster   14 

Fluctuating  variations  ...  268 

Fly  wings 230 

Focal  distance 513 

Foetus 215 

Food  cavity 171 

Food  solution     83 

Food-taking 440 

Food  tube    165 

Foot 78,  123,  126,  130,  I  57 

Forbes  quoted 51 


PAGE 

Fore  brain    199 

Fore  limbs  of  vertebrates  .      225 

Foresight   496 

Formic  acid 431 

Fourth  ventricle 192,  200 

Fragmentation    338 

Frog 275,  358,  362,466,485 

Fruit 148 

Funnel 166 


Galea    

Galls 7.  f/',  351. 

Gall  cyst 1S6, 

Gall  midge   42, 

Gall  wasps 43, 

Gallery 

Gamete 124,  138, 

Gametophyte    ....  124,  138, 

Gammarus 

Ganglion    190,  199, 

Gastric  glands 185, 

Gastrula 171,  194, 

Gastrulation    

Gelatine  solution 

Gemmules    

Genealogic  tree 

Genius  in  families 

Geographic  barriers    

Geographic  distribution  .  . 

Geranium 

Germ  cells    

Germ  plasm 291,320, 

Germinr-tion    


Ghost  stories 

Gill  arches    

Gill  chamber    

Gill  clefts 

Gill-pouches 

Gill  scoop 

Gills    

Gizzard  

Glands    

Glottis    183, 

Glosso-pharyngeal  nerve .  . 

Goldenrods    

Gomphus 

Gonangia    

Gonium    

Grafting 3<)o- 

Grafting  in  animals 


18 

524 
198 

352 

339 

52 
142 

152 

233 
448 

191 

255 

74 
334 
236 

321 

283 
284 

353 
299 

33^ 

505 
197 

411 

197 

259 

233 
411 

166 

169 

1S6 

463 
36 
356 
J  2  2 
106 

523 

^62 


53^ 


GENERAL  BIOLOGY 


PAGE 

Grafting  wax 523 

Grasshopper    113,  343 

Grasshopper  eggs    45 

Green  plants    370 

Gregarine 113 

Group  development    242 

Groups  of  organisms 220 

Group  radiation     239 

Growing  point 129 

Growth  habit 373 

Guard  cells 143 

Guest  gall-flies 45 

Guide  marks    • 33 

Guide  streaks 12 

Guinea  pigs    314 

Gymnosperms 152 

Gypsy  moth 399 

Gyrinus    386 

Habit    483 

Hemoglobin    177 

Hairs  of  bees    23 

Halesus    475,  476,  478 

Half  embryos 358 

Hand    486 

Harmony 509 

Hawk 480 

Head 17 

Head  Kidney 204 

Heart 187 

Heat 85 

Hemiptera 21,42,43,51 

Hemipterous  gall  makers  .        42 
Hemispheres  of  brain  .  .457,  462 

Heptagenia    244 

Herbivores 379 

Hereditary  diseases    318 

Heredity 259,  289 

Hermaphroditism 169 

Heterogeneous  inheritance     310 

Hertwig 209 

Hibernation 376 

Historical  documents  ....      492 

History  of  germ  cells 296 

Homology 223,  233,  258,  264 

Honey  bee 19 

Honey  dew 48,  5 1 

Hormones    443 

Horse 250 

Horsetail    , 136 


'  PAGE 

Host   396 

Human  brain 487 

Human  hand 486 

Human  population 326 

Human  species    48 5 

Humming-bird  flowers  ...         12 

Hunter  stage   495 

Husbandry     51, 496 

Hybrids 307,  311 

Hydra 157,  164,354,471 

Hydranth 330 

Hydroid 330 

Hydrophytes 372 

Hydroscopic  cells    136,  138 

Hyla 426 

Hymenium    96 

Hymenoptera    24,  42 

Hymenopterous  gall  makers     43 

Hyoid  apparatus 181 

Hyoid  bone    204 

Hyper-parasites    399 

Hypertrophy     367 

Ideal  condition  of  society  326 

Ids    301 

Imago 344 

Imitation 519 

Implements 496 

Incisor  teeth    259 

Inclusions    59 

Income 91 

Indian  com .  51 

Indian  pipe    397 

Infancy    489 

Infundibulum ...  200 

Inheritance 295 

Inheritance     of     acquired 

characters    318 

Insects 17 

Instincts 473 

Integuments    153 

Intensified  inheritance  ...  310 

Intercommunication    ....  ^42 

Interdependence 4,  7,  "68 

Intergradation     264 

Intermediate  forms 91 

Internal  gills    411 

Internal  secretions    44^ 

Intestine    107 

Inventor  stage ,  .  .  .  497 


INDEX 


5.37 


PAGE 

Iris II 

Iris  weevil    349 

Ischnura 387 

Isolation 502 

Jellyfish 331 

Joint-grass 137 

Juncos    429 

Jungermannia 124 

Juvenescence 329 

Karyokinesis 294 

Katabolism 90 

Kidney 184,  188 

Kinetic  energy 84 

Kinglet 476 

Kitten     480 

Labella     20 

Labium    18 

Labrum    18 

Lacinia 18 

Lack  of  insight     49 

Lactuca    40 

Lancelet 206,  214 

Language 489,  490 

Laughter    502 

Law  of  specialization    .  .  219,  422 

Leaf 130,  138,  143 

Learning  by  experience.  .  .      479 

Leaves  of  mosses 125 

Leeuwenhoek    299 

Legs    : 17 

Lemurs 485 

Leopard  frog 425 

Lepidoptera 24,  42,  44,  426 

Leptocephalus 343 

Lestes 376 

Leucocytes 173.  3  5° 

Libellula 285 

Lichen 390 

Lichen  buds 395 

Life  cycle    329 

Life  process 82,  176,  2  17 

Line  of  descent     291 

Line  of  succession    291 

Linin 293 

Linnaeus      220 

Lioness 321 

Liver 186,  198 


PAGE 

Liverwort 238 

Lloyd  Morgan  quoted  ...  364 

Loosestrife  , 13 

Lop-ears  in  rabbits 

Lorica 37 

Loss  of  color 4  :>  5 

Lost  api)endages 355 

Lungless  salamanders  ....  1S3 

Lymph  vessels 213 

Macrobiotus 377 

Macropis  ciiiata 8 

Macrosporangiuin 138,  i  50 

Macrospore    .  .  138,  140,  149,  153 

]\Iad  stone     505 

Magic 504 

Magnifying  power 513 

Malacostraca   230 

Malpighian  tubules 411 

Mammoth    4()^ 

Man    207 

]\Iandibles     18 

Mantle  galls 39 

Manual  training     487 

Marsh  hawks    324 

Marsupials 242 

Matter    82 

Maturation     297,  299 

Maxilla kS,  231 

]\Iaxillipeds    231 

Mayflies 244,  258,  347 

Meaning  of  nurture 321 

Mechanical  stimuli .^44 

Medulla    145,  192,  201 ,  461 

Medusa 330 

Meganucleus    7.=>.  '^o 

Mendel   310 

Mendelian  inheritance    ...      310 

Meristem    133 

Mesentery    iJS6 

Mesoderm     '  7  '  •  '  73-  '05 

Mesophytes 372 

Metabolism, 

86,  218.  329,  443.  457 
Metamorphosis    .  .  .342,  345.  352 

Metaphase    294 

Metazoa   441 

Metzneria 425 

Micrastcrias dS 

Micronucleus 75.  So 


538 


GENERAL  BIOLOGY 


PAGE 

Micropyle 150 

Microscope 517 

Microsporangia    138,  149 

Microspore 138,  149,  152 

Midges    351 

Milkweed  bug    429 

Mineral  salts    88 

Mimicry 429 

Mistletoe    505 

Mites 39 

Mitosis 294 

Mitotic  figures 295 

Mode 268 

Molanna 476 

Molds 95 

Money    496 

Monkeys 485,  490 

Monocotyledons    147 

Mononychus    379 

Morality 488 

Moral  person 510 

Mosaic    358 

Mosses    125 

Moth  ..21,36,426,456,469,476 

Motor  area 466 

Mouth-parts    17 

Mucor 95 

Mule 308 

Multi-cellular  reproductive 

bodies 334 

Multiple  receptors 446 

Muscle  cells    448 

Muscle  fibres 174,  441 

Muscles 161, 167 

Musk  turtle    322 

Mutation    273,317 

Mutual  sterility 286 

Mycelium 95 

Mycetozoa loi 

Myoneme 78,  80,  82 

Mysis    254 

Myxomycetes      loi 

Narcotics    506 

Nations    501,  502 

Native  population 326 

Natural  balance     -6,53,325,399 
Natural  selection, 

266,  267,  281,  283,  423,  497 

Natural  society   379 

Nature  and  nurture  ...318,    510 


PAGE 

Nauplius    257,343 

Necrophorus    428 

Nectar    7.ii 

Nematocysts   160 

Nematocytes 160 

Nematode    399 

Nephridium 166,  174,  184 

Nerve  and  muscle    448 

Nerve  cells 161,  172,  44 1 

Nerve  cord 449 

Nervous  system, 

165,  189,  451,  459,  460,487 

Nest  building 475 

Net   521 

Neural  folds 196 

Neural  tube    198 

Neurone 449 

Neuroterus 339 

Night  blooming  flowers    .  .         12 

Nitella    60,  62,  113 

Nitrogen  waste    177 

Nostoc    67 

Nostrils    183 

Nuclear  spindle 293 

Nucellus 150 

Nucleated  galls 40 

Nucleus    57 

Numerical  variation 272 

Nurture    318 

Nutrition   176 

Nymph 344 

Oak  .  ._ 4.  5.  36 

Objective  phenomena.  ...      436 
Oculo-motor  nerves      ....      463 

Olfactory  lobes    200 

Olfactory  nerve 463 

Oncopeltus 429 

Ontogeny 255,  358,  498 

Oocytes    297 

Oogones 296 

Operculum 126 

Optic  nerve    463 

Optic  lobes 192,  200 

Optic  ventricles 200 

Oral  groove    12> 

Orang 484,  485 

Organic  harmony    367 

Organism,  the  social     ....      500 
Organization   218 


IXDEX 


539 


PAGE 

Organs  of  out-reach    438 

Origin  of  species    277 

Orthogenesis 2 Si,  507 

Outgo 91 

Outlook    509,  511 

Ovary 122,  162,  188 

OverspeciaHzation    282 

Oviducts    189,  215 

Ovule 8,  150 

Ovule  case 8 

Ovum 112 

Palaeontology 246,  260,  492 

Palatine  teeth 183 

Palpus    18 

Pancreas    186,  198,  443 

Pandorina    107 

Parallelis-n 287 

Paralysis    466 

Paranioecium    .72,111,439,469 
Parasite.  .  .  .45.  5°.  252,  263,  356 

Parasitic  protozoans 113 

Parasitism 396 

Parenchyma    12c,  132 

Parthenogenesis    .  .  ^^c^.,  306,  339 

Pasteur 93 

Pasteur's  Solution 93 

Pastoral  stage 496 

Pectinatella 335 

Penicillium    95 

Pennaria    359 

Pentstemon 253 

Perianth 11 

Peristome 78 

Peritoneum 174 

Perla 244 

Persistence     of     the     un- 

specialized   250 

Petals 7-9 

Phagocytes    350 

Pharynx 165,  183,  197 

Philodina 378,  379 

Phloem 134,  145 

Phlox 26 

Phylloxera 362 

Phylogenetic  adaptation .  .      415 

Phylogeny    236,  255 

Phylum    236 

Physical  basis  of  racial  soli- 
darity        320 


PAGS 

Physcia    393 

Physiographic  barriers  .    .  285 

Pickhng 98 

Pike    275 

Pine    149 

Pineal  body 198,  200 

Pistachia    367 

Pistil 9 

Pituitary  body    200 

Pith    145 

Pitted  vessels 146 

Placenta 215 

Planarian 354,  523 

Plankton  net 521 

Plasticity  .  ■. 264 

Plasmodium    loi 

Play    499 

Plover 426 

Pocket  gall 40 

Polar  bodies 297 

Polarity 359 

Pollen 7,9,21,  402 

Pollen  basket 23 

Pollen  distribution 400 

Pollen  sacs i.\g 

Pollen  tube    9,1 50,  1 53 

Pollination 402 

Polyembryony    337 

Pond  animals 386 

Pond  life 385 

Pond  snails    523 

Pons 463 

Pores    120 

Post-em.bryonic     develop- 
ment    343 

Potato    7.361 

Potential  energy 84 

Pouched  mamma's 242 

Prairie    6 

Precava    iSS 

Preserves 98 

Pride  of  ancestry     321 

Primary  differentiation    ..  219 

Primary  food  of  animals    .  3 

Primary  germ  layers 171 

Primates    4S5 

Primitive  haunts 251 

Proboscides 19 

Process  of  evolution 266 

Progress  in  regression  ....  263 


540 


GENERAL  BIOLOGY 


PAGE 


Progressive  development        245 

Projection  fibers 463 

Pronephric  duct    206 

Pronephros    204 

Prophase    294 

ProstomiuiTL 163 

Proteins   83,  86 

ProthalHum 129,  138,  153 

Protoplasm,  57,  59,  88,  loi,  151, 

218,  290,  299,  435 

Protozoa.  .  68,  105,  221,  437,  441 

Psephenus  lecontei   244 

Pseudo-navicellae     115 

Pseudopodia 71,  103,  438 

Psocid  wings    230 

Psychic  phenomena'   436 

Psychic  states 434,  437 

Psyllidae    43 

Pteridophytes 128 

Pteris 129 

Pulmonary  circulation   ...      202 

Pupa 344,  347,  352,  362 

Pylorus 185 

Pyrenoids 62 

Quadrumana   485 

Quercus  macrocarpa 45 


Race  feeling 

Racial  differentiation   .... 

Racial  improvement 

Radial  symmetry    

Radiant  energy 

Rag  weed 

Rag  weed  seeds   ......... 

Reaping  machines 

Recapitulation    

Receptacle 

Receptors 436,  441 

Recessive  characters 

Reflex  arc     

Reflex  response 

Refraction    

Regeneration 3  53.  3  56 

Regeneration  in  cells    .... 

Regenerative  cells 

Regressive  development    . 

Reindeer  moss 

Relations  between  ants  and 
apliids 


286 
320 
328 
288 

84 
268 
269 

257 
265 

122 

.445 
310 
450 
457 
515 

.363 
357 
351 
251 
391 

47 


PAGE 

Reproduction    ....  109,  289,  329 

Reproductive  cells    122 

Reproductive  methods  ...      338 
Reproductive  organs    .  .  167,  188 

Resemblance 423 

Reserve  potentialities  ....      363 

Respiration  aquatic    213 

Retrogression    283 

Robber  fly 429 

Rhizoids 119,  120 

Rhizome 131,  136 

Rhus  glabra 37 

Riccia 124 

Root ',  .      130 

Root  louse .  ." 53 

Root  tubercles 99 

Rotifers    339,  378 

Sacculina 397 

Salamander   ..179,255,460,487 

Sandpiper    323 

Savages    497 

Scenodesmus 66 

Schultze 89 

Scion 360 

Scouring-rush    137 

Scroll  gall 40 

Sea  urchin  egg 291,357 

Secondary  circuits    454 

Secretin    443 

Secretions 59,  87,  443 

Seed    148,  151 

Seedlings    278 

Seed  plants    142,  152 

Seers 509 

Segmentation  cavity    ....      170 

Segments   17,231 

Segregation 283,331 

Selaginella 138 

Selection    339 

Self  pollination    10 

Senescence 329 

Sense  organs    444 

Sepals 9 

Sepedon   408 

Septa    165,  171 

Sequences  of  activities   ...      473 
Serial  homology    ..225,230,234 

Seta    164 

Sex  cells 167,  290 


INDEX 


541 


PAGE 

Gexual  reproduction, 

no,  1 12,  214,  331 

Sickle 251 

Sieve  tube    133 

Silica 137 

Silk  bolting  cloth 67 

Silk  glands 474 

Size 219,  381 

Skeleton 44S 

Skin  glands    183 

Skunk 429 

Slime  molds loi 

Slime-mold  Plasmodium    .      435 

Small  intestine     185 

Smell    444 

Snails 388 

Social  conduct 509 

Socialintegration 507 

Social  organism 507 

Society 379,  507,  509 

Song  Sparrow    284,  395 

Somatic  layer    172 

Soredia 395 

Sori 136 

Sound  receptors    447 

Sparrow   396 

Spathegaster    339 

Special  creation 264 

Specializatian 282 

Specialization  by  reduction     253 

Speech    502 

Sperm 1 12,  162 

Spermary  ....  122,  162,  168,  188 

Spermatogones 296 

Spermatophytes 142, 297 

Spermatozoan   112 

Sperm  cells 168 

Sperm  nuclei 149,  i  53 

Sperm  receptacles 167 

Spiders 471 

Spinal  column    180 

Spinal  cord 189,  196,  451 

Spinal  nerves 190 

Spinning  glands 475 

Spireme    293 

Spirogyra 60,  no 

Splanchnic  layer   172 

Spleen 186 

Sporangium  .  .  123,  126,  135,  138 
Spores  .  .  .  .97,  102,  115,  124,  126 


PA&E 

Spore  sacs    96 

Sporoganium 123 

Sporophores 95 

vSporophyte,   .  .  123,  126,  130,  135 

Sporozoa    112 

Spotted  salainander i  79 

Spreading  dogbane 366 

Squilla    233 

Shelter 4 

Smooth  sumac 271 

Stalk 123,  126 

Starch 85 

Starfishes 291 

Starling  quoted 490 

Statoblasts 334 

Steironema    8 

Stentor 76,  469 

Stem  borers   36 

Sterilization 98 

Stigma 9 

Stigmatic  surface    33 

Stimulants 506 

Stimulus 435,  444,  452 

Stipes 18 

Stock    -   T.to 

Stomach 185 

Stomach-intestine 166 

Stomates    127,  131, 143 

Stone  ax 490 

Stoneflies 244 

Stone  knives    491 

Stone  worts 113 

Strap  lichen   392 

Stratification 373 

Struggle  for  existence  ....      276 

Strychnine 468 

Style 9 

Sub-intestinal  vessel 165 

Sugar    94 

Sumac 36,  270 

Sunfish 275 

Supporting  tissues    132 

Survival  of  the  fittest    .  .  2  76,  456 

Swallow 243 

Swift 243 

S  wanning 522 

Swarm  spores    333 

Symbiosis 390,  400 

Symbols 490 

Symmetry 288 


542 


GENERAL  BIOLOGY 


PAGE 

Sympathetic  system  .  .  .  190,  460 

Synapsis 303 

Synergid  nuclei    153 

Synthesis    84 

Synthetic  types 248 

Syrphidae   432 

System  of  classification    ..  222 

Systems  of  organs 442 

Tails  of  sheep 319 

Tannin 38 

Tardigrades 377 

Tarsus    243 

Teeth    127,  183 

Telophase 294 

Telson 231 

Tentacles   157 

Tenthredinidae    44 

Terrestrial  life   121 

Testes 188 

Thallophytes 118 

Thallus 119,129 

Third  ventricle    200 

Thoracic  duct      213 

Thorax 17, 232 

Thyroid  gland   443 

Time  adjustments    375 

Tipula 229 

Tongue 183 

Toolsj 491 

Tool  using    487,  490 

Torulae 92 

Toti-potent  sperm  nucleus     304 

Touch 444,  446 

Tracheae    1S7,  259,  408 

Tracheal  gills 409 

Tracheid 133 

Transformation  of  insects343,347 

Tree  frog    426,427 

Trial  and  error 481 

Tribal  societies    501 

Types  of  inheritance 30S 

T3^pes  of  nurture 214 

Types  of  symmetry 2SS 

Uppe^jbrain 481 

..Uretef 18S,  206 

Ctrin^ry  bladder    186,  198 

C<.Vtenis    189,  2 1 5 

J^-'Utricularia 252 

Vacuole    58 

^^      Vagus 191,  463 

^  ^'9^11  Beneden 299 


PAGE 

Variation   267,  268,  289 

Vascular  bundles 132,  143 

Vaucheria    65 

Veins    259 

Velvet 365 

Venation  of  leaf 135 

Venous  sini;s 187 

Ventricle    187 

Vertebra 180 

Vertebrate  characters  ....      195 
Vestigial  structures  .  .  .  .259,  265 

Vesture 21 

Vibrations 446 

Vibratorv  stimulus 453 

VilH  .  .  .  .' 185,  215 

Viola  cucullata    ^7, 

Violet   33,  152 

Vision 445 

Vital  relations   7 

Vol  vox   107,  112 

Von  Baer   174 

Vorticella 76,  79 

Vorticellidae    81 

Wars 326 

Warning  coloration /49 

Wasp    _ 490 

Water  and  distribution    ..      372 

Water  penny   245 

Water  vessels 492 

Weaklings    279 

Web    4 

Weevil    5.  3  79 

Whirligig 3S7 

Willow 11,45,352 

Wind,  effects  of    401 

Wings     17,225,258 

Wing  veins 225,229,258 

Winter  buds 334 

Witch  hazel  aphid 341 

Witches'  broom 37 

Wood 145,  146 

Woodland  plant  society  ..      373 

Xerophytes    372 

Xylem    145 

Yeast 92 

Yolk  plug 194 

Zoaea 343 

Zoochlorellaj 394 

Zoospore     333. . 34° 

Zoothamnium 81 

Zygote    297 


